JP

The role of natural variability in projections of climate change impacts on U.S. ozone pollution

Climate change can impact air quality by altering atmospheric conditions that determine pollutant concentrations. Over large regions of the U.S., projected changes in climate are expected to favor formation of ground-level ozone and aggravate associated health effects. However, modeling studies exploring air quality-climate interactions have often overlooked the role of natural variability, a major source of uncertainty in projections. Here we use the largest ensemble simulation of climate-induced changes in air quality generated to date to assess the influence of natural variability on estimates of climate change impacts on U.S. ozone. We find that internal variability can significantly alter the robustness of projections of the future climate’s effect on ozone pollution. In this study, we find that a 15-year minimum is required to identify to identify a distinct anthropogenic-forced signal. Therefore, we suggest that studies assessing air quality impacts use multidecadal simulations or initial condition ensembles. With natural variability, impacts attributable to climate may be difficult to discern before midcentury or under stabilization scenarios.

Assessing climate change impacts, benefits of mitigation, and uncertainties on major global forest regions under multiple socioeconomic and emissions scenarios

We analyze a set of simulations to assess the impact of climate change on global forests where MC2 dynamic global vegetation model (DGVM) was run with climate simulations from the MIT Integrated Global System Model-Community Atmosphere Model (IGSM-CAM) modeling framework. The core study relies on an ensemble of climate simulations under two emissions scenarios: a business-as-usual reference scenario (REF) analogous to the IPCC RCP8.5 scenario, and a greenhouse gas mitigation scenario, called POL3.7, which is in between the IPCC RCP2.6 and RCP4.5 scenarios, and is consistent with a 2ºC global mean warming from pre-industrial by 2100. Evaluating the outcomes of both climate change scenarios in the MC2 model shows that the carbon stocks of most forests around the world increased, with the greatest gains in tropical forest regions. Temperate forest regions are projected to see strong increases in productivity offset by carbon loss to fire. The greatest cost of mitigation in terms of effects on forest carbon stocks are projected to be borne by regions in the southern hemisphere. We compare three sources of uncertainty in climate change impacts on the world's forests: emissions scenarios, the global system climate response (i.e., climate sensitivity), and natural variability. The role of natural variability on changes in forest carbon and net primary productivity (NPP) is small, but it is substantial for impacts of wildfire. Forest productivity under the REF scenario benefits substantially from the CO2 fertilization effect and that higher warming alone does not necessarily increase global forest carbon levels. Our analysis underlines why using an ensemble of climate simulations is necessary to derive robust estimates of the benefits of greenhouse gas mitigation. It also demonstrates that constraining estimates of climate sensitivity and advancing our understanding of CO2 fertilization effects may considerably reduce the range of projections.

Climate model uncertainty in impact assessments for agriculture: A multi-ensemble case study on maize in sub-Saharan Africa

Almost 25 percent of the world’s malnourished population lives in sub-Saharan Africa (SSA), and depends on maize (corn) for much of its caloric intake. The most widely produced crop by harvested area in SSA, maize is also highly sensitive to drought. Because maize in this region is grown largely on rain-fed rather than irrigated land, any future changes in precipitation patterns due to climate change could significantly impact crop yields. Assessing the likely magnitude and locations of such yield changes in the coming decades will be critical for decision-makers seeking to help their nations and regions adapt to climate change and minimize threats to food security and rural economies that are heavily dependent on agriculture.

Toward that end, a team of five researchers with the MIT Joint Program on the Science and Policy of Global Change has applied a broad range of multi- and individual climate model ensembles to project climate-related changes to maize yields throughout most of the 21st century. Accounting for uncertainty in climate model parameters—which is pronounced in high-producing semiarid zones—the researchers project widespread yield losses in the Sahel region and Southern Africa, insignificant change in Central Africa, and sub-regional increases in East Africa and at the southern tip of the continent. The wide range of results highlights a need for risk management strategies that are adaptive and robust to uncertainty, such as the diversification of rural economies beyond the agricultural sector.

The results appear in the early online edition of the journal Earth’s Future. Funded by MIT’s Abdul Latif Jameel World Water and Food Security Lab as a two-year project, “Advancing Water and Food Sustainability through Improved Understanding of Uncertainties in Climate Change and Climate Variability,” the study’s principal investigators are Susan Solomon, Lee and Geraldine Martin Professor of Environmental Studies in the Department of Earth, Atmospheric and Planetary Sciences; and Kenneth Strzepek, research scientist in the MIT Joint Program.

Save the date for the 16th annual Henry W. Kendall Memorial Lecture Series honoring the memory of Professor Henry W. Kendall (1926-1999) who was the J.A. Stratton professor of physics at MIT. Professor Kendall received the Nobel Prize in 1990 for research that provided the first experimental evidence for quarks. He had a deep commitment to understanding and finding solutions to the multiple environmental problems facing the world today and in the future.

16th Annual Kendall Lecture with Thomas R. Karl - "Climate Data: Mysteries, Wonders, and Reality"

On March 8 in Helsinki, Finland, MIT Joint Program Deputy Director Sergey Paltsev delivered a keynote address on energy policy and the new U.S. administration at a seminar on oil and geopolitics hosted by the Finnish Institute of International Affairs and World Energy Council Finland. In his presentation, Paltsev explored the kinds of policies that the new U.S. administration is likely to pursue, and prospects for keeping up U.S. unconventional oil production under continuous low prices.  

Energy and the new U.S. administration

Judges of the American Association for the Advancement of Science (AAAS) 2017 Student Poster Competition selected a poster by MIT Joint Program research assistant Michael Davidson as the winner in the Social Sciences category. Davidson’s poster was one of 15 presented in that category at the AAAS Annual Meeting in Washington, D.C. in February.

Michael Davidson scores winning poster in Social Sciences category in 2017 AAAS Student Poster Competition

In September 2015, the German Volkswagen Group, the world’s largest car producer, admitted to having installed “defeat devices” in 11 million diesel cars sold worldwide between 2008 and 2015. The devices were designed to detect and adapt to laboratory tests, making the cars appear to comply with environmental standards when, in fact, they emitted pollutants called nitric oxides, or NOx, at levels that were on average four times the applicable European test-stand limit.

Study: Volkswagen’s excess emissions will lead to 1,200 premature deaths in Europe

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