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Web Special Rising temperatures, swelling seas, and the threat to life forms are all linked to climate change. Down To Earth documents the possibilities…
RITU GUPTA
Several degrees of change
Studies have documented the adverse impacts of climate change worldwide
The heat is on
Both oceanic and terrestrial temperatures are rising
Melting into oblivion
The snow cover worldwide has been decreasing at an unnatural pace
Sea change
The sea is swelling slowly, crossing the danger mark
The conveyor belt
The adverse impacts could also change the climates
Rain in Spain always fall on the plain…
…Not any more
Is this a blessing?
Climate change could increase the intensity of monsoons
Weather really unfair
The world will witness more extreme weather events as the temperature rises
Hitting the food web
Climate change would impact the flora and fauna in ways that can't be perceived
Impact on fauna
Polar bear could disappear within 100 years unless global warming is abated
Unhealthy weather
Overall, climate change means more disease burden
A threat to food security
Rising temperatures mean less crop yield in most developing countries
More tremors, less freshwater
Retreating glaciers in southern Alaska may cause earthquakes, say researchers
Impact on coral reefs
Australia’s Great Barrier Reef poised to lose 95 per cent of its living coral by 2050
Several degrees of change
Studies have documented the adverse impacts of climate change worldwide
Things that normally happen in geologic times are happening during the span of a human lifetime — this is the scientific perception of global warming. Moreover, even seemingly small perturbations can cause the climate to swing rapidly and drastically. Data from ice cores taken from Greenland and elsewhere reveal that parts of the planet cooled by 10°C in just a few decades about 12,700 years ago. Five thousand years ago, the Sahara region of Africa was transformed from a verdant lake-studded landscape like Minnesota’s to barren desert in just a few hundred years. The Earth’s history is full of such abrupt changes in response to climate change.Although at present we are only at an early stage of the projected global warming, ecological responses to rising temperatures are clearly visible. Scientists and policymakers who think that global warming is too remote to worry about, something projected by the same computer techniques that often can’t get next week’s weather right, should think again, rather just observe. From Alaska to the snowy peaks of Andes, the projections are coming true, in the form of melting glaciers and even genetic changes in flora and fauna. Here are some ‘scientific perceptions’, which may be out of the sight of a common person, but not out of the minds of scientists. Some of them are region–specific changes, but they spell out the omen of what’s in store for the whole planet.
The heat is on
Both oceanic and terrestrial temperatures are rising
According to the report of the Intergovernmental Panel on Climate Change (IPCC), the global average surface temperature has increased by 0.6 ± 0.2°C since the late 19th century. It is very likely that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record since 1861. Most of the increase since the late 19th century has occurred in two distinct periods: 1910 to 1945 and since 1976. The rate of increase of temperature for both the periods is about 0.15°C per decade. Recent warming has been greater over land compared to oceans. The increase in sea surface temperature over the period 1950-1993 is about half the increase in the mean of surface air temperature.The most recent warning about the rising temperatures comes from a report by the Geneva-based World Meteorological Organisation (WMO) dated December 15, 2004. “The global mean surface temperature in 2004 is expected to be 0.44°C more than the 1961-1990 annual average (14°C), states the report that is based on an analysis of temperature records maintained by WMO’s member countries. This value of 0.44°C places 2004 as the fourth warmest year since 1861 just behind 2003 (+0.49°C). However, 1998 remains the warmest year, when surface temperatures averaged +0.54°C above the 30-year mean. The last 10 years (1995-2004), with the exception of 1996, are among the warmest 10 years on record.
Region-specific trends also prove that the temperatures are rising. A study published in the March 5, 2004 issue of the journal Science shows that during the late 20th and early 21st century, European climate has been warmer than any time during the past 500 years, and 2003 was by far the hottest summer. These findings are important considering that Europe has been increasingly experiencing extreme weather events during the past decade.
IPCC predicts that over the period 1990 to 2100, global average surface may increase by 1.4-5.8°C. In the December 5, 2003 issue of the journal Science, two leading scientists of the US, after reviewing extensive literature estimated that between 1990 and 2100, global temperatures would rise by 1.7°C to 4.9°C. “Even if society decreases its emissions considerably, the temperatures would still increase by about 0.5°C over a period of decades because greenhouse gases (GHGS) take decades to cycle out of the atmosphere,” wrote Thomas Karl of the National Climatic Data Centre and Kevin Trenberth of the National Centre for Atmospheric Research.
Melting into oblivion
The snow cover worldwide has been decreasing at an unnatural pace
When the temperatures rise, the first impact can be observed on ice and snow. According to the IPCC report, satellite data shows that there has been a decrease of about 10 per cent in the extent of snow cover since the late 1960s; ground-based observations show a reduction of about two weeks in the annual duration of lake and river ice cover in the mid and high latitudes of the Northern Hemisphere over the 20th century. The region’s spring and summer sea ice extent has decreased by about 10-15 per cent since the 1950s. In the Arctic, during the recent decades there has been about a 40 per cent decline in the sea ice thickness during the late summer to early autumn phase.Everywhere on earth ice is undergoing metamorphosis. The famed snows in Kilimanjaro have melted more than 80 per cent since 1912. The Qori Kalis glacier in Peru is shrinking at a rate of 200 metres per year, 40 times faster than the rates in 1978. Glaciers in the Garhwal Himalayas are retreating so fast that researchers believe they will disappear by 2035. Arctic sea ice has thinned significantly over the past half century, and its extent has declined by about 10 per cent in the past 30 years. Repeated laser altimeter readings of the US National Aeronautical and Space Administration (NASA) show that the edges of Greenland’s ice sheet shrinking. Spring freshwater ice break-up in the Northern Hemisphere now occurs nine days earlier than it did 150 years ago, and autumn freeze up to 10 days later. Thawing permafrost has caused ground to subside more than 10 feet in parts of Alaska. From Arctic to Peru, from Switzerland to the equatorial glaciers of Irian Jaya in Indonesia, massive ice fields, monstrous glaciers, and sea ice are disappearing, fast. The largest contribution to sea level rise is coming from the Alaskan glaciers — an estimated 23 cubic miles of water.
The IPCC report projects that Greenland ice sheet is likely to lose mass during the 21st century and contribute a few centimetres to sea level rise even if the climate has stabilised. Climate models indicate that warming over the Greenland is likely to be one to three times the global average. As per ice sheet models, if a local warming of more than 3°C were to be sustained for millennia, it would lead to virtually a complete melting of the Greenland with a resulting sea level rise of about seven metres.
Antarctica ice sheets are likely to gain mass during the 21st century, as per IPCC. But a study by scientists from NASA, published in the journal Science dated September 14, 2004, shows that the Antarctic glaciers are thinning and slipping ever faster into the sea. Glaciologist Robert Thomas led a team that flew over to West Antarctica in 2002 and measured the thickness of six glaciers flowing into the Amundsen Sea with radar. He found the glaciers were thinning at twice the rate they had in the 1990s, when a European satellite measured them. The glaciers are losing about 250 cubic kilometres of ice to the ocean each year — about 60 per cent more ice than they accumulate from snowfall. That translates to a global sea level rise of 0.2 millimetres a year — equivalent to 10 per cent of the current rising levels.
Sea change
The sea is swelling slowly, crossing the danger mark
When ice melts, more water flows into the seas from glaciers and ice caps. A rise in temperatures also expands the oceans water in volume. The combination of these effects has played a major role in raising average global sea level. According to the IPCC report, analysis of tide ‘gauge’ data shows that global average sea level rose between 0.1 and 0.2 metres (m) during the 20th century. But despite these findings, the issue was much debated, as estimates from tide gauges show a rise of 0.0015-0.002 metres per year, whereas assessment based on the two processes responsible for global sea level rise — namely mass and volume change of waterbodies — fall far below this range. Estimates of volume increase due to ocean warming give a rate of about 0.0005 m per year and the rate due to mass increase resulting from the melting of continental ice, is thought to be even smaller. Therefore, many experts had argued that either the tide gauge estimates are too high, or one (or both) of the mass and volume estimates is too low.A study, published in the journal Nature dated March 25, 2004, resolved this debate. Researchers from the US-based National Oceanic and Atmospheric Administration and Florida International University conducted the study. The researchers analysed sea level measurements of tide gauges combined with observations of temperature and salinity in the Pacific and Atlantic oceans. They found that gauge-determined rates of sea level rise are correct. More importantly, mass increase (due to melting glaciers) has played a greater role than ocean warming in the 20th century global sea rise.
Another study published in the journal Geophysical Research Letters dated April 26, 2004 uncovered a bizarre effect — the sea seems to be rising faster near the coast than in mid-ocean. Simon Holgate and Philip Woodworth of the Proudman Oceanographic Laboratory, the UK, found this discrepancy using data of the Topex satellite, launched in 1992. The satellite measures sea level by bouncing microwaves off the ocean and timing the return trip. According to the Topex data, global average sea level rose by 0.0028 metres a year between 1993 and 2002. But during the same period, the water level within 100 kilometres of the coast rose faster, by an average of 0.0037 millimetres a year. Holgate and Woodworth concluded that the oceans were behaving like water in a bathtub — if you splash in the bath, waves travel outwards and then run around the edges of the tub. In fact, in 1996, ocean modellers predicted that this effect could be at work in the seas: when ocean heats up, the water expands, creating waves that hit the coast then travel around the rim of the ocean basin for several years. Holgate and Woodworth are the first to document this actually happening. Their findings are bad news for the many millions of people who live near the shore, as the global warming increasing the difference between coast and ocean could get worse, and flooding could be an even bigger problem than scientists have anticipated.
The future projections of IPCC provide more reasons to worry. Global mean sea level is projected to rise by 0.09 to 0.88 m between 1990 and 2100. For the periods 1990 to 2025 and 1990 to 2050, the IPCC projections are a rise of 0.03 to 0.14 m and 0.05 to 0.32 m respectively.
Moreover, these projections sea levels may be just the tip of the iceberg. In the July 19, 2002 issue of the journal Science, researchers have found that the Alaskan glaciers (mountains around the Gulf of Alaska comprising up to 90,000 square kilometre of glacier area) produce more meltwater than previously allowed for in models. Future sea level changes therefore may be underestimated. These glaciers are estimated to contribute to half the expected sea level rise.
These rising sea levels will in particular devastate the poor. Rich nations are prepared to spend up to US $32 billion to protect the European coastline from sea level rise, but have promised only US $0.41 billion to help poor nations confront climate change, according to a report launched by pressure groups Greenpeace and the New Economic Foundation during the latest round of climate change talks held in Argentina. The gap is alarming, as the cost of defending the coastline of just one nation, Tanzania, from a one metre rise in sea level could total more than US $14 billion.
Rising sea level produces a cascade of effects. More than a hundred million people worldwide live within three feet of mean sea level. Vulnerable to sea level rise, Tuvalu, a small country in the South Pacific, has already begun formulating evacuation plans. Mega cities where human populations have concentrated near costal plains or river deltas — Shanghai, Bangkok, Jakarta, Tokyo and New York — may all be submerged. The projected economic and humanitarian impacts on low-lying, densely populated, and desperately poor countries like Bangladesh are potentially catastrophic. The scenarios are even disturbing for wealthy countries like the Netherlands, with nearly half its landmass already at or below sea level. Bruce Douglas, a coastal researcher at the Florida International University, calculates that every inch of sea level rise could result in eight feet of horizontal retreat of sandy beach shorelines due to erosion. Furthermore when salt water intrudes into freshwater aquifers, it threatens sources of drinking water and makes raising crops problematic. For instance, in the Nile delta, where many of Egypt’s crops are cultivated, widespread erosion and saltwater intrusion would be disastrous, since the country contains little other arable land. In some places the marvels of human engineering are already threatened by the rising seas, Venice being is the most perfect example.
The conveyor belt
The adverse impacts could also change the climates
Rising sea level is not the only change Earth’s oceans are undergoing. The 10-year-long World Ocean circulation Experiment launched in 1990 has helped researchers better understand what is now called the ocean conveyor belt. Oceans, in effect, mimic some functions of the human circulatory system. Just as arteries carry oxygenated blood from the heart to the extremities, and veins return blood to be replenished wit oxygen, oceans provide life-sustaining circulation to the planet. Propelled mainly by prevailing winds and differences in water density, which changes with the temperature and salinity of the sea water, oceans currents are critical in cooling, warming, and watering the planet’s terrestrial surfaces — and in transferring heat from the Equator to the Poles.The engine running the conveyor belt is the density-driven thermohaline circulation (thermo = heat, haline = salt). Warm, salty water flows from the tropical Atlantic north towards the Pole in surface currents like the Gulf Stream. This saline water loses heat to the air as it is carried to the far reaches of the North Atlantic. The coldness and high salinity together makes the water denser, and it sinks deep into the ocean. Surface water moves in to replace it. The deep, cold water flows into the South Atlantic, Indian and Pacific Oceans, eventually mixing again with warm water and rising back to the surface.
Thus, the conveyor belt is driven by cold, salty water in the Arctic, which sinks to the bottom and flows south. If the water isn’t salty enough to sink, the conveyor belt shuts down. Now, scientists are discovering that Arctic and North Atlantic waters are becoming fresher because of increased precipitation and melting. “Over the past four decades, the subpolar North Atlantic has become dramatically less salty, while the tropical oceans have become saltier,” observed William B Curry of the US-based Woods Hole Oceanographic Institution in a recent congressional testimony. “These salinity changes are unprecedented in the relatively short history of the science of oceanography.”
Without the conveyor belt, Europe and the northeastern US will be far colder. The conveyor belt had stopped in the past, as recent as 8,200 years ago. A recent Pentagon report tells of a “plausible…though not the most likely” scenario, in which the conveyor belt shuts off. “Such abrupt climate change…could potentially destabilise geopolitical environment, leading to skirmishes, battles, and even war,” warns the report.
Rain in Spain always fall on the plain…
…Not any more
In January 2003, rainfall patterns of Lesotho — a small region in Africa — altered suddenly, ushering in untimely frost and severe storms that destroyed most of the standing crops. “Frost in summertime! We never used to see weather like this,” said Makhabasha Ntaote, a 71-year-old matriarch.Makhabasha is not the only one flabbergasted by the changing patterns of rainfall. Worldwide, the showers have been defying the weather forecast. As per the WMO report, 2004 was the wettest year since 2000. Wetter-than-average conditions prevailed in the southern and eastern US, eastern Europe and parts of western Asia, Bangladesh, Japan and coastal Brazil. Flooding in northeast India (Assam and Bihar in particular) and Bangladesh was the worst in over a decade. In October 2004, two typhoons and active frontal systems brought record-breaking heavy rainfall to Japan. Tokyo received a total amount of 780 millimetres precipitation, which is the largest monthly amount on record since 1876.
Heavy rains from mid-January to March in areas of Angola produced flooding along the river system, which flows into neighbouring Zambia, Botswana and Namibia. Extensive flooding along the Zambezi River, the worst flooding since 1958, threatened more than 20 000 people in northeastern Namibia and caused extensive damage to crops.
These are vital signs of what’s in store. As per the IPCC report, precipitation has increased by 0.5-1 per cent per decade in the 20th century over most mid and high latitudes of the Northern Hemisphere continents; over the tropical (10°N to 10°S) land areas, there was an increased of 0.2 to 0.3 per cent a decade, but over much of the Northern Hemisphere sub-tropical (10°N to 30°N) land areas, there was a decrease of around 0.3 per cent per decade. No comparable systematic changes have been observed in broad latitudinal averages over the Southern Hemisphere.
A latest research depicts a universal scenario, which is scary. The study, led by Beate Liepert of the Lamont-Doherty Earth Observatory at Columbia University, USA, was published in the journal Geophysical Research Letters, dated May 20, 2004. As per the findings, incoming solar radiation is being trapped in a layer of clouds and aerosols, thereby decreasing the amount of radiation that would ordinarily hit the Earth’s surface. This imbalance of less solar radiation with warming surface temperatures is leading to weaker turbulent heat fluxes resulting in reduction in evaporation and precipitation, which in turn implies a dryer world.
Although rising temperatures should moisten the atmosphere, the research shows that human-made airborne aerosols are condensing the water to form smaller cloud droplets. This process is contributing to the observed thickening of the Earth's cloud cover. Smaller droplets are not heavy enough to sink through the air as rain. As a result, the cloud cover lasts longer and there is less rain. “Water has a characteristic residence time in the atmosphere before it gets rained out. In a warmer world, this residence time is longer because a warmer atmosphere can hold more water. Aerosols affect clouds by suppressing rain and increasing its residence time. The overall effect is that rainwater is about half a day older,” explains Liepert. Data supporting this hypothesis include studies indicating a steady decline of water evaporation in the Northern Hemisphere over the past 50 years.
Is this a blessing?
Climate change could increase the intensity of monsoons
A research published in the journal Science provides the much-needed insight into the correlation between the intensity of monsoons and rising temperatures. The Southwest Asian monsoon is one of the most important climate systems on Earth affecting nearly half of the world’s population every year. Through seasonal reversal in winds and hence moisture transport, it supplies much-needed precipitation during the summer months to countries like India, Bangladesh and China.The research from the US-based University of Colorado, University of Arizona, USA, and Indian Institute of Technology, Kharagpur, reveals several distinctive trends in monsoons strength between 1000 and 1986 AD in response to the changing climes. Particularly interesting is an increase in monsoon intensity from 1600 AD through the present. This time period spans the Little Ice Age (~1550 to 1850 AD), when the Northern Hemisphere experienced a cold spell, and also covers the last century, during which anthropogenic effects may have begun to influence global climate. The study authors found that the minimum in monsoon strength shortly after 1600 AD coincides with the Maunder Minimum, a period of reduced solar activity. It appears to represent the weakest monsoon of the last 10,000 years. The authors also discovered a link between a weakened southwest monsoon and cooler conditions in the North Atlantic and Eurasia. They suggest that large-scale cooling during the Little Ice Age affected the monsoons.
On the other hand, they found that monsoon was stronger during the earlier part of the record, the so-called Medieval Warm Period (~1000 to 1350 AD) than during the 20th century. Several terrestrial pollen records from China and Tibet indicated stronger precipitation during the Medieval Warm Period.
From their findings, the researchers inferred that the northern hemispheric temperature variability controls the Southwest Asian monsoon. This argument has critical implications in the face of global warming. Their monsoon record broadly resembles reconstructed Northern Hemisphere temperature changes, including a pronounced increase in monsoon intensity during the past century.
Temperature is clearly an important influence on monsoon variability. But does the monsoon respond only to hemispheric temperature changes, or is even driven by local, direct forcing mechanisms such rising levels of GHGs. The question remains unanswered. As the authors note, their record does not have sufficient ‘temporal resolution’ to discriminate between the influences of these forces.
The researchers took their research a step further, and published a paper in the January 23, 2003 issue of the journal Nature. They found there is also a link between the climate in the North Atlantic region and monsoons. Their monsoon proxy records showed several intervals of weak summer monsoon that coincide with cold periods documented in the North Atlantic region — including the most recent climate changes from the Medieval Warm Period to the little Ice Age and to the present.
From both the results one fact is clear — a cold weather leads to a weaker monsoon, whereas warmer temperatures increase its intensity. Hence, global warming is bound to leave its imprint on monsoons. But neither too less nor too much of monsoons is good. A decrease in the Southwest Asian monsoon led to widespread famine in the late 19th century. A much-increased monsoon caused by global warming would have equally serious consequences. Too much rain results in severe flooding and soil erosion.
Weather really unfair
The world will witness more extreme weather events as the mercury risesPick up any textbook on hurricanes and it will tell you that the one place where hurricanes do not occur is the South Atlantic Ocean. The atmosphere does not provide enough spin near the surface to get them started and winds higher in the atmosphere tend to shear off any that do make a start. Hence, it was with some amazement that meteorologists watched the first ever-recorded hurricane develop off the coast of Brazil in the last week of March in 2004. It came ashore in the Brazilian state of Santa Catarina on March 28, 2004 with winds, causing much damage to property and loss of life. The Brazilian meteorologists dubbed it 'Catarina'.
It is now well established that global warming implies more of such unexpected extreme weather events. According to the December 2004 WMO report, an exceptional heat wave affected much of eastern Australia during February, as maximum temperatures soared to 45°C in many areas. The spatial and temporal extent of the heat wave was greater than that of any other February heat wave on record.
In 2003, instead of confining itself to issuing scientific reports and statistics at the end of each year, WMO was forced to bring out a report in August 2003 due to the extreme oddities of weather patterns such as pre-monsoon heat wave in India resulting in the death of 1,400 people. At least 562 tornadoes had hit the US in May 2003, killing 40 people. This was much higher than the previous peak of 399 storms recorded during 1992. To date, the 10 hottest years in the 143-year-old global temperature record has been have all been after 1990. Extreme weather events have also increased during these times. There were 63 weather-related disasters declarations in 1998, far more than the average 21.78 disaster announcements made per year during the 1980s.
With the weather becoming more unpredictable, both human causalities and economic losses have increased. In the 1980s, the world’s property insurers lost an average of US $2 billion annually to extreme weather events. But in the 1990s, losses exceeded US $12 billion per year. For just the first 10 months of 1998, weather-related expenses (US $89 billion) far exceeded the losses for the entire decade of 1980s. Poor nations tend to suffer more than the wealthier ones — while flooding in Mozambique cut the country’s gross domestic product (GDP) by 45 per cent in 2000, floods of the same scale in Germany in 2002 were blamed for just one per cent decline in the nation’s GDP.
According to scientists, in the near future, such weather-related disasters would become quite common. Heat waves in Chicago, Paris and elsewhere in North America and Europe will become more intense, more frequent and longer lasting in the 21st century, according to a new modelling study by two scientists at the National Centre for Atmospheric Research, USA. In the US, heat waves will become most severe in the West and South, the scientists reported in the August 13. 2004 issue of the journal Science. Gerald Meehl and Claudia Tebaldi examined Earth’s future climate using the Parallel Climate Model. Its results show that an increase in heat-absorbing GHGs intensifies an unusual atmospheric circulation pattern already observed during heat waves in Europe and North America. As the pattern becomes more pronounced, severe heat waves occur in the Mediterranean region and the southern and western US. Parts of France, Germany and the Balkans also become more susceptible to severe heat waves.
A study by researchers from the UK-based Hadley Centre for Climate Prediction and Research, University of Reading and University of Oxford states that emissions of GHGs has doubled the risk of extreme heat waves, such as the 2003 one that killed 20,000 people, in Europe. “The summer of 2003 was the hottest in Europe since the 1500 AD,” the researchers write in their paper published in the journal Nature dated December 2, 2004. “These kind of studies will help the affected people seek compensation from big polluters. Claims linked to climate could far exceed the billion-dollar compensation given by tobacco companies,” asserted Peter Roderick, director of the Climate Justice Programme, in the wake of the study.
Hitting the food web
Climate change would impact the flora and fauna in ways that can’t be perceived
There is ample evidence of the impacts of the recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organisational hierarchies, from the species to the community levels.Phenology — the timing of seasonal activities of animals and plants — is the simplest process to track changes in the ecology of species in response to climate change. Animals, plants and insects are already adapting to climate change by shifting their ranges, advancing migrating dates, and altering timings of mating and flowering. A study of 35 non-migratory butterfly species in Europe found that in recent decades about two-thirds have expanded their ranges northward by 32 to 241 kilometres. Many plants in Europe flower about a week earlier than they did 50 years ago and shed their leaves in the fall five days later. British birds breed on an average nine days earlier than in the 20th century, and frogs mate up to seven weeks sooner. Tree swallows in North America migrate north in spring 12 days earlier than they did a quarter century ago. Red foxes in Canada are shifting their ranges hundreds of miles toward the Pole, moving into the territories of Arctic foxes. Alpine plants are edging uphill and beginning to overrun rare species near mountain summits. In Europe, leaf colour changes show progressive delay of 0.3-1.6 days per decade, whereas the length of the growing season had increased in some areas by up to 3.6 says per decade over the past 50 years.
A study published in the March 2004 issue of the journal Nature shows that Amazonian rainforests have experienced changes in dynamics and composition in the last two decades. Of the 115 relatively abundant tree genera studied, 27 changed significantly in population density — a value nearly 14 times greater than that expected by chance. Genera of faster-growing trees, including many canopy species, are increasing in dominance and density, whereas genera of slower-growing trees, including many sub-canopy species, are declining.
Climate change impacts individual species as well as the entire food chain. Since different species react to climate change in different ways, the natural cycles of interdependent creatures — such as birds and the insects they feed on — may fall out of sync, causing population declines.
For now, as much of the world warms, animals and plants can try to beat the heat by retreating to higher altitudes and elevations. But such escape routes have limits, some of them imposed by humans. “During the past major climate changes, there wasn’t a lot of human disturbance. But this is no longer the case,” says Camille Parmesan, an ecologist at the University of Texas, USA. She conducted a study highlighting the pressure that species face when squeezed between warming world and habitat destruction. In a 300-mile swath of territory between northern Mexico and southern California, the Edith’s checkerspot butterfly has become extinct in 80 per cent of its historical range. The major cause, Parmesan showed, has been rising temperatures, which have led to the early desiccation of host snapdragon plants, depriving the butterfly larvae of crucial nutrition.
In January 2004, researchers from the University of Rhode Island found that some songbirds may avoid eating insects that consume leaves exposed to high levels of CO2. “When plants are grown in conditions of higher CO2, they produce increased levels of several secondary compounds — tannins and phenolics — that they use as a defence against herbivores,” said Martina Müller, the lead author of the study, adding: “Those secondary compounds are absorbed by gypsy moth caterpillars that feed on the plant’s leaves, which other researchers have found reduces the caterpillar's growth rates. We wanted to see if the chickadees can detect the secondary compounds in the caterpillars and if they have preferences for caterpillars that fed on different types of leaves.”
Using chickadees captured in Kingston and acclimated for three days, the researchers fed the birds a choice of caterpillars that were high in tannins or phenolics and other caterpillars low in those compounds. “It was clear that the birds could tell the difference between the different caterpillars and they had strong preferences,” Müller said. The birds showed a distinct preference for caterpillars low in tannins and phenolics.
Changes in breeding patterns not only affect species, but also the way they interact. For instance, winter warming has precipitated breeding season changes in some but not alls species of amphibians in Britain. This variability has immediate consequences for species interactions. Thus, newts are entering ponds earlier than before, whereas frogs have not substantially altered their reproductive timings. Embryos and larvae of early-breeding frogs are, therefore, exposed to higher levels of newt predation. Such examples illustrate the high order consequences of responses to climate change. Another example being the delays in spring arrival by migratory birds that is leading to increased competition for nest sites with species arriving earlier. Evidence also indicates that warmer spring weather in Europe has disrupted the synchrony between winter moth (Operophtera brumata) hatching and oak bud burst, leading to a mismatch between the peak in insect availability and the peak food demands of great tit (Parus major) nestlings.
Individual shifts sometimes have had no overall negative impact. But in other cases, they have made survival tougher as the large-scale movements bring new species into contact with each other, often resulting in direct competition, such as appears to be occurring as the competitively superior red fox pushes the arctic fox farther towards the sea.
Moreover, flora and fauna populations may adapt to the changing atmosphere, but the evolved communities are likely to be genetically less strong than their contemporaries. In the September 2004 issue of the journal Nature, researchers from McGill University of Canada report a long-term selection experiment that they conducted to investigate the phenotypic consequences of selection for growth at elevated CO2 concentrations. After about 1,000 generations, selection lines of the unicellular green alga Chlamydomonas failed to evolve specific adaptations to a CO2 concentration of 1,050 parts per million. Some lines, however, evolved a syndrome involving high rates of photosynthesis and respiration, combined worth higher chlorophyll content and reduced cell size.
Another study by researchers from Carnegie Institution and Stanford University shows that though warming, increased precipitation and nitrogen deposition, have increased net primary production in the California grasslands, elevated CO2 levels are suppressing root formation, decreasing the positive effects.
Such changes may finally lead to the extinction of many species, shows a research from the University of Leeds and Centre for Applied Biodiversity Science, published in the January 7, 2004 edition of the journal Nature. As per the findings, climate change could drive more than a quarter of land animals and plants into extinction. As per the study, climate change projected to take place between now and 2050 will place 15 to 37 per cent of all species in several biodiversity-rich regions at risk of extinction. The researchers considered three different climate scenarios were considered — minimal, mid-range and maximum. Species ability to successfully disperse or move to different areas was also taken into consideration. The researchers found that minimum expected, or inevitable, climate change scenarios for 2050 produce fewer projected extinctions (18 per cent) than mid-range projections (24 per cent) and about half of those predicted under maximum expected climate change (35 per cent).
Impact on fauna in a nutshell
Polar bear could disappear within 100 years unless global warming is abated
In the Lake Constance region of central Europe, which includes parts of Germany, Austria and Switzerland, researchers determined number of land bird species and the abundance of each species during two census periods (1980-81 and 1990-92). The researchers studied 300 species and divided them into three categories: residents, short-distance migrants (600 to 1,200 miles) and long-distance migrants (more than 2,200 miles). There were 122, 80, 108 species in each category respectively. Climate did not affect the resident and short-distance migratory birds. Buy as the average temperature of the coldest month increased by more than four degrees F, the abundance of the long-distance migratory birds decreased by one fifth.Researchers from Stanford University have found that animals that thrive in high temperatures are less likely to survive global warming than those that are less tolerant to heat. For instance, porcelain crabs in the cool Pacific Northwest have the ability to adjust to larger increases in habitat temperatures than crabs living in the warm coastal water of Mexico. Reason — the cold-water crabs are able to change their upper thermal tolerance limit much more readily than those from hotter climes.
Polar bear could disappear within 100 years unless global warming is abated. University of Alberta researchers found that Arctic ice — the bear’s primary habitat — is melting faster than believed.
Warmer ocean temperatures have adversely affected the population of the tufted puffin seabirds in western Canada. Uncharacteristically warm sea surface temperatures have persisted near Triangle Island — a haven for these birds. Since 1975, years with very high temperatures have coincided with incidences of no chicks being raised. “The puffin’s prey — small fish — leave areas with warm water. Then adult puffins abandon their chicks under these circumstances to forage further up shore. With the chicks left to starve, the species population I bound to decline,” says researchers from the University of Alberta.
Due to global warming, loggerhead sea turtles have started laying their eggs about 10 days earlier than they did 15 years ago. In 2003, half of the turtles’ nests were laid before June 19. In 1989, they did so on June 29.
As per biologists from the University of Alberta, claimte change will cause the nortern limit of the winter range of the North American little brown bar (Myotis lucifugus) to extend northward by approximately five kilometres per year over the next century.
Research from the University of California links extinction of 30 species of the desert bighorn ships with the rising temperatures. The researchers evaluated the impacts of range of factors, including disease outbreak, poaching and mining. “Climate was consistently correlated with extinction in a way other factors were not,” the researchers wrote in the journal Conservation Biology.
Rising ocean temperatures have led to a decline in the stocks of fish in the North Atlantic Ocean. Researchers from Sir Alister Hardy Foundation for Ocean Science investigated the impact on the marine food web of varying water temperatures and wind strengths in the North Atlantic. They found that the fluctuations in the abundance, size and composition of plankton result in long-term changes in the numbers of large, commercially important fish, such as North sea cod.
A common Great plains prairie plant, the partridge pea (Chamaecrista fasciculata) could face severe reduction in numbers if climate conditions in the US Midwest becomes drier and warmer. “The various genes that contribute to drought tolerance tend not to occur in individual plants,” says R Eterson of the University of Minnesota, USA. If the partridge pea is threatened, then other native species may also be facing the same fate.
Unhealthy weather
Overall, climate change means more disease burden
Change in world climate would have impacts on human health. Some of these impacts would be beneficial. For example, milder winters would reduce the seasonal winter-time peak in deaths that occurs in temperate countries, while in hot regions further increase in temperatures might reduce the viability of disease-transmitting mosquito populations. Overall, however, scientists consider that most of the health impacts of climate change would be adverse.The World Health Organisation estimated in its ‘World Health Report 2002’ that climate change was responsible in 2000 for approximately 2.4 per cent of worldwide diarrhoea and six per cent malaria in some middle-income countries and seven per cent of dengue fever in some industrialised countries. In total, the attributable mortality was 154 000 (0.3 per cent of the total) deaths and the attributable burden was 5.5 million DALYs (0.4 per cent of the total).
As per the IPCC report, overall climate change is projected to increase threats to human health, particularly in lower income populations predominantly within tropical subtropical countries. Climate change can affect human health through multiple pathways, including direct affects (such as increased heat stress, loss of life in floods) and indirect effects that operate through changes in the ranges of disease vectors (example mosquitoes), water-borne pathogens, water quality air quality, food availability and quality among other things.
The IPCC report concludes that climate change would cause increased heat-related mortality and morbidity, decreased cold-related mortality in temperate countries, greater frequency of infectious disease epidemics following floods and storms, and substantial health effects following population displacement from sea level rise and increased storm activity. For instance, the annual excess summer-time mortality in the US attributable by 2050 is estimated to increase seven fold. A study ‘Potential effect of population and climate changes on global distribution of dengue fever: an empirical model’, published in the Lancet in 2002 (p 830-834), shows that small temperature increases can greatly affect transmission potential of malaria. Globally, temperature increases of 2-3°C would increase the number of people who, in climatic terms, are at risk of malaria by around 3 to 5 per cent (that is several hundred million). Further, the seasonal duration of malaria would increase in many currently endemic areas. Modelling studies also suggest that a warming projection of 2°C by 2100 will result in a net increase in the potential latitudinal and altitudinal range of dengue and an increase in transmission season in temperate locations. Changes in potential transmissions in areas that currently are endemic are projected to be limited.
A threat to food security
Rising temperatures mean less crop yield in most developing countries
Agriculture would be affected by climate change as rising temperatures would affect water supply and soil nutrient availability among other things. As per the IPCC report, if global mean temperature change from the year 1990 is 0.4-1.1°C by 2025, then cereal crop yield will increase in many mid and high latitude regions, but will decrease in most tropical and subtropical regions. If global mean temperature change from the year 1990 is 0.8-2.6°C by 2050, then there will be mixed effects on cereal yields in mid latitudes regions, and incomes of poor farmers in developing countries would decrease. More pronounced cereal yield decreases in tropical and sun-tropical regions. If global mean temperature change from the year 1990 is 1.4-5.8°C by 2100, then there will be a general reduction in cereal yields in most mid-latitude regions.Rice yields may already be crashing at twice the rate predicted by climate modellers, according to the first ‘real world’ experiment of the impacts of rising temperatures conducted by researchers from the International Rice Research Institute (IRRI), the Philippines. The results suggest that global rice yields could potentially fall by a catastrophic 50 per cent during this century. The study found that a 0.7°C increase in the mean daily temperature was associated with a rice yield decrease of 10 per cent. Past predictions of future rice yields have forecast declines of five per cent for an increase of 0.7°C. According to IRRI researchers, these predictions are low because they missed the fact that global warming is most intense at night, when tropical plants need to cool off and respire.
However, some people believe that global warming should be good for crop yields. The veteran British TV botanist and environmentalist David Bellamy recently grabbed headlines by saying that plants should grow faster in a greenhouse world because the extra CO2 will make photosynthesis more efficient. IRRI researchers agree by saying that the increased CO2 concentration should partly offset the negative effects of higher night-time temperatures, but they point out that the their research plots have been subjected to both higher temperatures and higher CO2 levels, and the negative effects won.
Not only will the developing countries be affected, but also the industrialised world. Computer-based simulations of US agriculture show that, by the year 2060, the benefits of climate change to American croplands could be less than previous work had indicated. A team of scientists from the National Centre for Atmospheric Research and several universities found that finer-scale simulations tend to reduce projected benefits and increase projected losses for a wide range of crops across most parts of the nation.
The team compared present-day conditions to scenarios for a doubled level of atmospheric carbon dioxide, which will occur around 2060 if present trends continue. The results reveal that crop productivity in general across the Great Plains and Mississippi Delta increases, but it lowers for many crops elsewhere. For instance, previous work found that corn harvests should decrease by 2060 in the Midwest's Corn Belt and Southeast but increase in the Northern Plains. The latest finer-scale study accentuates both trends. In economic terms, the previous coarse-scale analysis had showed that climate change could benefit US agriculture in the year 2060 by roughly US $3 billion, even assuming that farmers did not adapt their planting to accommodate the climate shifts. The finer-scale analysis reduces the figure to around US $0.3 billion.
More tremors, less freshwater
Retreating glaciers in southern Alaska may cause earthquakes, say researchers
In the September 23, 2004 issue of the journal Nature, researchers report about the findings of the long-term experiment in the Arctic. The researchers dug deep into the carbon balance of an artic tundra ecosystem, and came up with surprising results. Their research reveals that tundra plants and soils respond in opposing ways to long-term nutrient fertilisation. In their experiment, intended to simulate increased nutrient availability under warmer temperatures, plants grew better and stored more carbon, but valuable soil carbon was lost. In the context of global warming, the main implication of their findings is that the losses of deep-soil carbon could mean even greater increases in carbon dioxide concentrations in the atmosphere.NASA and US Geological Survey scientists found that retreating glaciers in southern Alaska may be opening the way for future earthquakes. As glaciers melt they lighten the load on the Earth’s crust. Tectonic plates, that are mobile pieces of the Earth's crust, can then move more freely and collide. The colliding plates create a great deal of pressure that builds up, and eventually is relieved by earthquakes “Historically, when big ice masses started to retreat, the number of earthquakes increased. Therefore, our theory holds water,” the researchers say.
With temperatures rising, average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by seven per cent from 1936 to 1999. The average annual rate of increase was 2.0±0.7 cubic kilometres per year.
Freshwater will be in ever-shorter supply as climate change gathers pace. Veteran climate modeller Syukuro Manabe and his colleagues from the US-based Princeton University simulated what effect a quadrupling of atmospheric carbon dioxide (CO2) from the pre-industrial levels would have on the global hydrological cycle over the next 300 years. They found that both evaporation and precipitation would increase. Evaporation will reduce the moisture content of soils in many semi-arid parts of the world, including northeast China, the grasslands of Africa, the Mediterranean and the southern and western coasts of Australia. With increase in precipitation, the overall discharge of freshwater from rivers around the world to rise by almost 15 per cent. The biggest increases will be in the thinly populated tropics and the far north of Canada and Russia. For instance, the flow of the river Ob in Siberia is projected to increase by 42 per cent by the end of the 23rd century. But there will be lower flows in many mid-latitude rivers, which run through heavily populated regions. Those that will start to decline include the Mississippi, Mekong and especially the Nile, one of the world's most heavily used and politically contested rivers, where his model predicts an 18 per cent fall in flow.
Impact on coral reefs
Australia’s Great Barrier Reef poised to lose 95 per cent of its living coral by 2050
Global climate change poses a major threat to the world’s coral reefs, which already are suffering from coastal development, over-fishing and pollution. A report warns that changes in surface ocean temperature and chemistry will continue to damage these biologically vital and economically important ecosystems. For instance, the famous Great Barrier Reef of Australia will lose 95 per cent of its living coral by 2050.The UK-based Pew Centre on Global Climate Change report, ‘Coral Reefs & Global Climate Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems’, analyses the likely impacts of climate change over the next century on coral reef ecosystems around the world.
Scientists are finding that global warming endangers reefs in two important ways. First, higher water temperatures are promoting coral bleaching — episodes in which corals and other reef-building species are weakened or killed after losing vital algae that lives within their tissues. Although coral species can recover from bleaching to some degree, repeated bleaching events are likely to eliminate sensitive organisms and reduce biodiversity. Elevated water temperatures are also thought to be a factor in the recent increase in coral diseases in the Caribbean.
Second, as carbon dioxide builds up in the atmosphere, more of it is dissolved into the ocean, which increases ocean acidity. This lowers concentrations of the carbonate ion, a building block of calcium carbonate that corals and other organisms use to grow their skeletons and build up the reefs. Carbon dioxide levels in the atmosphere, which were about 280 parts per million by volume (ppmv) in 1880, increased to 367 ppmv by 2000 and are expected to reach from 463 to 623 ppmv by 2050. An increase to 560 ppmv would cause an estimated 30 per cent reduction in the carbonate ion concentration in the upper ocean and affect both skeletal growth rates and the structural growth of reefs.
The Pew report notes that coral reefs are among the most biologically diverse ecosystems on Earth, providing vital habitat to numerous species as well as economic benefits to society in the form of fishing and tourism. One recent estimate concluded the world's reefs provide annual net economic benefits of $30 billion.
