The physical risks of climate change are not just looming in the future but have already become very evident today. Projections of rising global temperatures in a just-released World Meteorological Organization report, along with observations from recent years, underscore that the climate system is not static but moving to greater and greater extremes. The 10 warmest years recorded with thermometers since records began in 1880 (140 years ago) all occur within the last 16 years. These changing global warming statistics patterns are reflected at the regional level, as evidenced by the total domination of dark red “record warm” pixels over dark blue “record cold” pixels (none) in NOAA’s regional temperature map for 2020.
Moreover, the year 2020 (a La Niña year) has approximately tied 2016 (an El Niño year) as the record warmest year. Why is that a surprise? Because La Niña years are generally cooler and El Niño years are generally warmer than usual. La Niña and El Niño conditions, along with volcanos (cooling) and other natural variations, add year-to-year variability to the otherwise monotonic global warming driven by greenhouse gases and other air pollutants.
Along with surface-level warming, the Earth’s atmosphere is becoming more humid, and climate extremes more intense and frequent. Arctic summer sea ice is disappearing more quickly; the Greenland and Antarctic ice sheets are receding faster; tropical cyclones are intensifying and moving more slowly, creating larger storm surges and precipitation events and more severe flooding; and droughts, extreme heat events and wildfires are intensifying. These trends, on scales from local to global, are now impacting — and in coming decades likely to further impact — vulnerable infrastructure, supply chains and human health, and to induce widespread famine and migration.
There is now substantial evidence that achieving the world’s aggressive, long-term goal of keeping the global average surface temperature increase well below 2 degrees Celsius from its preindustrial level will dramatically reduce the physical risks posed by climate change. While the long-term goals of the Paris Agreement suggest that world leaders have taken these physical risks seriously, the near-term targets in the accord are largely not on track to meet those long-term goals without a substantial change in direction starting now.
At the same time, efforts to move the world toward net-zero emissions in alignment with the 2 degrees Celsius goal come with major new local-to-global “transition” risks and accompanying challenges that must be met. This transition involves shifts on political, social, technological and economic fronts, and presents new challenges for financing and economies, from stranded fossil-fuel assets to stranded workers needing retraining. We will need to strike the optimal balance between the risk of over-investing in the near term in today’s green technologies that will ultimately be superseded, versus the risk of under-investing in these technologies and subsequently needing to rapidly reduce greenhouse gas emissions with the resultant economic shocks.
Lowering these transition risks toward net-zero-emissions economies will involve integration of both physical and transitional components, a process that requires new and improved models and frameworks. The goal is to empower decision-makers in government and industry to lower the transition risks as an integral companion to mitigation strategies. Financial institutions and regulators will also need to get involved. Finally, we will need to invest more and more in adaptation along with mitigation to lower overall climate risks.
To frame future studies of physical and transition risks, MIT’s just-released 2021 Global Change Outlook provides probabilistic climate and socio-economic projections obtained using updated probability distributions for key parameters in both the human- and Earth-system components of our Integrated Global System Modeling (IGSM) framework.
These projections provide insight into the probability of outcomes of interest, including emissions, concentrations, temperature, precipitation, GDP and energy. The 2021 Outlook also presents prospects for achieving the Paris Agreement’s short-term targets (as defined by Nationally Determined Contributions, or NDCs) and long-term goals of keeping the increase in the average global temperature below 2 degrees Celsius or even 1.5 degrees.
Finally, the solutions to these challenges need to be affordable and equitable for all people and all nations. The poorest countries are the most vulnerable and the least responsible for climate change. And the COVID-19 pandemic superimposed on climate change has exposed the compounding effects of multiple stressors on these same vulnerable populations.
Ronald Prinn, Sc.D, is a professor of atmospheric sciences at MIT and director of MIT’s Joint Program on the Science and Policy of Global Change and Center for Global Change Science. Prinn’s research interests incorporate the chemistry, dynamics and physics of the atmospheres of the Earth and other planets and the chemical evolution of atmospheres.