The climate’s sensitivity to carbon dioxide – how much the temperature rises with a certain increase of emissions – is now better understood. This new knowledge indicates that moderate emission reductions are less likely to meet the Paris climate targets than previously anticipated.
The climate’s sensitivity to carbon dioxide – how much the temperature rises with a certain increase of emissions – is now better understood. This new knowledge indicates that moderate emission reductions are less likely to meet the Paris climate targets than previously anticipated.
- Earth’s temperature response to doubling the levels of carbon dioxide in the atmosphere is now better understood. While previous IPCC assessments have used an estimated range of 1.5–4.5°C, recent research now suggests a narrower range of 2.3–4.5°C.
- This means that moderate emissions reduction scenarios are less likely to meet the Paris temperature targets than previously anticipated.
- Improved regional scale models provide better information about heavy rainfall events and hot and cold extremes, offering new opportunities for water resource management.
- Regional climate predictions can now be made up to a decade ahead with higher skill than previously thought possible.
- Earth’s temperature response to doubling the levels of carbon dioxide in the atmosphere is now better understood. While previous IPCC assessments have used an estimated range of 1.5–4.5°C, recent research now suggests a narrower range of 2.3–4.5°C.
- This means that moderate emissions reduction scenarios are less likely to meet the Paris temperature targets than previously anticipated.
- Improved regional scale models provide better information about heavy rainfall events and hot and cold extremes, offering new opportunities for water resource management.
- Regional climate predictions can now be made up to a decade ahead with higher skill than previously thought possible.
The climate effect of CO2 is commonly expressed by the equilibrium climate sensitivity, which is the long-term global rise in air temperature expected as a result of doubling atmospheric CO2 concentrations. The “likely range” (at least a 66% chance of being within this range) of equilibrium climate sensitivity was estimated to be 1.5–4.5°C by IPCC in its Fifth Assessment Report (AR5). These figures have remained unchanged since the Charney report of 1979.
A new comprehensive analysis of the broader evidence has now narrowed the likely range to 2.3–4.5°C. This analysis shows that a low climate sensitivity below 2.3°C is unlikely (less than 33% chance), which discounts the lower end of the IPCC AR5 range. This conclusion indicates that moderate emissions reduction scenarios are less likely to meet the Paris temperature targets than previously anticipated.
At the other end of the range, a larger climate sensitivity had been suggested by recent global-scale climate change experiments coordinated under the Coupled Model Intercomparison Project Phase 6, CMIP6 (which is set up to compare the models underpinning IPCC AR6). The Earth System models included there exhibit sensitivity values ranging from 1.8–5.6°C. The values for ten of these models exceeded 4.5°C. But many of these high-sensitivity models overestimated recent warming trends, suggesting their results should be treated with caution.
Evidence against the high sensitivities is provided from three sources: examining climate feedback processes, the historical record, and the paleoclimate (prehistoric climate) record, which counter the high model climate sensitivities. In particular, they found that sensitivities above 4.5°C are hard to reconcile with paleoclimate evidence.
On regional scales, climate models are now better at simulating temperature and hydrological extremes, including the intensity of heavy rainfall events and hot and cold extremes. Models can now simulate rainfall droughts well, particularly at the seasonal scale, and the projections of drought duration and frequency are becoming more consistent over many regions, even though regional changes in mean rainfall remain uncertain. The improvements provide new opportunities for national and regional water resource management.
In the near term, climate models are now better at predicting the observed evolution of regional climate than previously thought possible, particularly around the Atlantic Basin. Decadal predictions of the atmospheric circulation and regional temperature and rainfall all now show encouraging levels of skill, offering great promise for the utility of regional climate predictions.
The climate effect of CO2 is commonly expressed by the equilibrium climate sensitivity, which is the long-term global rise in air temperature expected as a result of doubling atmospheric CO2 concentrations. The “likely range” (at least a 66% chance of being within this range) of equilibrium climate sensitivity was estimated to be 1.5–4.5°C by IPCC in its Fifth Assessment Report (AR5). These figures have remained unchanged since the Charney report of 1979.
A new comprehensive analysis of the broader evidence has now narrowed the likely range to 2.3–4.5°C. This analysis shows that a low climate sensitivity below 2.3°C is unlikely (less than 33% chance), which discounts the lower end of the IPCC AR5 range. This conclusion indicates that moderate emissions reduction scenarios are less likely to meet the Paris temperature targets than previously anticipated.
At the other end of the range, a larger climate sensitivity had been suggested by recent global-scale climate change experiments coordinated under the Coupled Model Intercomparison Project Phase 6, CMIP6 (which is set up to compare the models underpinning IPCC AR6). The Earth System models included there exhibit sensitivity values ranging from 1.8–5.6°C. The values for ten of these models exceeded 4.5°C. But many of these high-sensitivity models overestimated recent warming trends, suggesting their results should be treated with caution.
Evidence against the high sensitivities is provided from three sources: examining climate feedback processes, the historical record, and the paleoclimate (prehistoric climate) record, which counter the high model climate sensitivities. In particular, they found that sensitivities above 4.5°C are hard to reconcile with paleoclimate evidence.
On regional scales, climate models are now better at simulating temperature and hydrological extremes, including the intensity of heavy rainfall events and hot and cold extremes. Models can now simulate rainfall droughts well, particularly at the seasonal scale, and the projections of drought duration and frequency are becoming more consistent over many regions, even though regional changes in mean rainfall remain uncertain. The improvements provide new opportunities for national and regional water resource management.
In the near term, climate models are now better at predicting the observed evolution of regional climate than previously thought possible, particularly around the Atlantic Basin. Decadal predictions of the atmospheric circulation and regional temperature and rainfall all now show encouraging levels of skill, offering great promise for the utility of regional climate predictions.
- Energy sector planning, for understanding vulnerabilities under different energy mixes, planning future wind farm sites or developing resource management strategies.
- For water utilities, who have identified the need for improved climate information using decadal time scales for their planning. Decadal forecasts are particularly important in countries with an uneven distribution of water resources, such as India and China, that are facing increasing demands from the agriculture sector.
- Energy sector planning, for understanding vulnerabilities under different energy mixes, planning future wind farm sites or developing resource management strategies.
- For water utilities, who have identified the need for improved climate information using decadal time scales for their planning. Decadal forecasts are particularly important in countries with an uneven distribution of water resources, such as India and China, that are facing increasing demands from the agriculture sector.
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