At current rate of emissions, the world is set to breach the global warming limit of 1.5 degrees Celsius between 2030 and 2052, reveals the IPCC Special Report on the impacts of global warming of 1.5°C. At present, the world is 1.2°C warmer compared to pre-industrial levels. The special report, which was commissioned to specifically explore the scientific feasibility of the 1.5°C goal set in the Paris Agreement, suggests progressive worsening of extreme weather events as temperature rises.
By 2100, global mean sea level rise is projected to be around 0.1 metre lower if the global warming is restricted to 1.5°C compared to 2°C.
Adaptation needs will also be lower for global warming of 1.5°C. It implies that limiting global warming to 1.5°C compared to 2°C is projected to lower the impacts on terrestrial, freshwater, and coastal ecosystems and retain more of their services to humans.
To limit global warming to 1.5°C, net-zero emissions would have to be achieved by 2050 and emissions would need to be drastically cut by at least 45 per cent by 2030. The corresponding rates of reduction to limit warming to 2°C would require a 20 per cent reduction by 2030 and net-zero emissions by 2075.
The report provides clarity on the burning question of carbon budget: how much carbon can we continue to emit if we are to abide by the Paris Agreement? By the end of 2017, anthropogenic CO2 emissions since the preindustrial period are estimated to have reduced the total carbon budget for 1.5°C by approximately 2200 ± 320 GtCO2eq (gigatonne of CO2 equivalent).
Currently, humans emit 42 ± 3 GtCO2 eq per year. When researchers considered global mean surface air temperature in models, they found that we have a budget of 580 GtCO2eq for a 50 per cent probability of limiting warming to 1.5°C, and 420 GtCO2eq for a 66 per cent probability. Models using global mean surface temperature, instead, threw up remaining budgets for 1.5°C as 770 and 570 GtCO2eq respectively for 50 per cent and 66 per cent probabilities of limiting the temperature rise to 1.5°C.
Researchers have estimated uncertainties in climate response to CO2 and non-CO2 emissions, which could contribute ±400 GtCO2eq while the level of historic warming contributes ±250 GtCO2. The amount of carbon that will be released will thaw permafrost, and wetlands methane emissions would reduce budgets by up to 100 GtCO2eq over the course of this century and more thereafter.
Estimates of the global emissions outcome of current nationally stated mitigation ambitions as submitted under the Paris Agreement would lead to global greenhouse gas emissions of 52–58 GtCO2eq per year in 2030. The science shows that current climate efforts would not limit global warming to 1.5°C, even if they are supplemented by an increase in the scale and ambition of emissions reduction after 2030.
According to the report, while meeting the 1.5°C warming goal is improbable, it is not impossible. Meeting the objectives of the Paris Agreement would inevitably have to involve carbon dioxide removal from the atmosphere. All pathways, which limit global warming to 1.5°C or allow a minimal breach, project the use of carbon dioxide removal (CDR) to the tune of 100–1000 GtCO2eq over this century. It implies that achieving the target purely by reducing emission is extremely improbable; investment will have to move towards active removal through afforestation, carbon capture and storage, and other novel technologies.
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