Contributions by Emissions from Various Regions to the Global Energy Budget

In 2009, Susan Solomon co-authored with me a paper on the energy balance of the Earth. This paper showed how ocean heat content could be combined with global temperature records to produce a balanced energy budget for climate change. In turn, this energy budget put constraints on the total climate effect of aerosols. Ten years later, and updated energy budget still shows similar patterns to the one we made in 2009.

One of the lessons of working with an energy budget is that for some questions it can be more informative to compare energy (Joules) rather than radiative forcing (Watts when integrated over the area of the Earth). One such question is how the emissions from various regions contribute to climate change. Integrating over time the radiative forcing caused by emissions of carbon dioxide and other species shows the contribution of that region to the Earth’s energy budget. Several patterns stand out from such calculations.

Some regions have had a common historical pattern in which the short-term offsets between the radiative forcings from carbon dioxide and sulfate aerosols temporarily led to near-zero radiative forcing during periods of exponential emissions growth with few emission controls. This happened for North America and Europe in the mid-20th century and China in the 1990s and 2000s. However, these same periods lead to a commitment to future radiative forcing from the carbon dioxide and other greenhouse gases that stay in the atmosphere long after the aerosols. For every region, this commitment to future cumulative radiative forcing (2018–2100) from emissions already in the atmosphere is larger than the cumulative radiative forcing to date (1900–2017). North America has had the largest contribution to the Earth’s energy budget to date. Which region has the largest future contribution depends on future emission scenarios.