Global temperatures are rising due to the accumulation of greenhouse gases in the atmosphere. In addition to increasing greenhouse gas emissions, human activity has changed the composition of particles in the atmosphere. These have masked some of the warming caused by the greenhouse gases. How large is this cooling effect, and how has it changed over time?
In the UTRICS project the temporal development of the cooling effect of aerosols will be studied to improve estimates of climate sensitivity.
Climate sensitivity is a key concept in climate research that represents the temperature rise for a given increase in CO2 concentration. The large uncertainty in the climate sensitivity is a key topic in climate research and vital for our understanding of the severity of global warming. The complex feedback processes in the climate system make it difficult to determine how sensitive the Earth is to increases in greenhouse gases, and thus how stringent mitigation measures are needed to keep warming below 2°C or even 1.5°C.
To improve the knowledge of future climate change, we must increase our understanding of past drivers of climate change. The UTRICS project investigates the temporal development of the aerosol effective radiative forcing, that historically have masked part of the warming due to the increase in greenhouse gases. Results of detailed aerosol modeling, taking advantages of international multi-model initiatives, analysis of aerosol observations, as well as in-house simulations, will be combined with observational based time series of global temperature and ocean heat content using an established method, to infer estimates of aerosol ERF time series and climate sensitivity.
The project group has previously published estimates of climate sensitivity and showed in 2018 that the time development of the aerosol cooling was crucial for the climate sensitivity estimate. In this project, uncertainty in the time development of aerosol radiative forcing will be quantified and uncertainty in the time development will be implemented in the method for estimating climate sensitivity.
Our method is a necessary complement to earth system models, both with respect to the highly parameterized processes related to the climate feedbacks and to aerosol and aerosol cloud interaction in the models.
With a better estimate of aerosols radiative forcing and climate sensitivity in combination with scenario data, we will illustrate the uncertainties in global temperature change over the coming decades. This is essential for the goal in the Paris Agreement to limit warming to below 2 or 1.5°C.
UTRICS represents the next step in observational based estimates of climate sensitivity, by taking into account the uncertainties in aerosol forcing time development.
Full name of project: Understanding Temporal aerosol Radiative forcing - Implications for Climate Sensitivity and future warming.
Duration and founding: Financed by the Research Council of Norway. The project will run for 4 years, from 1 August 2021 and until 31 July 2025. More info about the project can be found here.
Project partner: Norwegian Computing Center.