Regional Analysis

Twenty-First-Century Changes in U.S. Regional Heavy Precipitation Frequency Based on Resolved Atmospheric Patterns

Precipitation-gauge observations and atmospheric reanalysis are combined to develop an analogue method for detecting heavy precipitation events based on prevailing large-scale atmospheric conditions. Combinations of atmospheric variables for circulation (geopotential height and wind vector) and moisture (surface specific humidity, column and up to 500-hPa precipitable water) are examined to construct analogue schemes for the winter [December–February (DJF)] of the “Pacific Coast California” (PCCA) region and the summer [June–August (JJA)] of the Midwestern United States (MWST). The detection diagnostics of analogue schemes are calibrated with 1979–2005 and validated with 2006–14 NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA). All analogue schemes are found to significantly improve upon MERRA precipitation in characterizing the occurrence and interannual variations of observed heavy precipitation events in the MWST. When evaluated with the late twentieth-century climate model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), all analogue schemes produce model medians of heavy precipitation frequency that are more consistent with observations and have smaller intermodel discrepancies than model-based precipitation. Under the representative concentration pathways (RCP) 4.5 and 8.5 scenarios, the CMIP5-based analogue schemes produce trends in heavy precipitation occurrence through the twenty-first century that are consistent with model-based precipitation, but with smaller intermodel disparity. The median trends in heavy precipitation frequency are positive for DJF over PCCA but are slightly negative for JJA over MWST. Overall, the analyses highlight the potential of the analogue as a powerful diagnostic tool for model deficiencies and its complementarity to an evaluation of heavy precipitation frequency based on model precipitation alone.

Nearly 25 percent of the world’s malnourished population lives in sub-Saharan Africa, where more than 300 million people depend on corn, or maize, as their main food source. Maize is the most widely harvested agricultural product in Africa and is grown by small farmers who rely heavily on rainwater rather than irrigation. The crop is therefore extremely sensitive to drought, and since 2015 its production has fallen dramatically as a result of record-setting drought conditions across southern and eastern Africa. 

Climate change to worsen drought, diminish corn yields in Africa
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.

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.

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

Gas-to-liquids (GTL), a process that converts natural gas to liquid fuels such as gasoline, diesel and jet fuel rather than producing these fuels from crude oil, has barely penetrated the energy market, with fewer than 10 industrial-scale plants currently in operation around the world. For decades, the relative cost of crude oil to natural gas has limited investment in GTL, but persistently low U.S. natural gas prices in recent years have boosted this ratio to an all-time-high, leading investors to reconsider the potential of GTL.

Is there a future for gas-to-liquids technology?
Carbon emissions in China: How far can new efforts bend the curve?

While China is on track to meet its global climate commitments through 2020, China’s post-2020 CO2 emissions trajectory is highly uncertain, with projections varying widely across studies. Over the past year, the Chinese government has announced new policy directives to deepen economic reform, protect the environment, and limit fossil energy use in China. To evaluate how new policy directives could affect energy and climate change outcomes, we simulate two levels of policy effort—a Continued Effort scenario that extends current policies beyond 2020 and an Accelerated Effort scenario that reflects newly announced policies—on the evolution of China’s energy and economic system over the next several decades. Importantly, we find that both levels of policy effort would bend down the CO2 emissions trajectory before 2050 without undermining economic development, although coal use and CO2 emissions peak about 10 years earlier in the Accelerated Effort scenario.

One of the two top air pollutants in the U.S., ground-level ozone is harmful not only to your health but also to your bank balance. Long-term exposure to high concentrations of ozone can lead to respiratory and lung disease such as asthma, conditions that drive up medical expenses and sometimes result in lost income. Ozone exacts a particularly heavy toll on people living in economically disadvantaged areas, where industrial and power plants tend to cluster.

Modeling the unequal benefits of U.S. environmental policy

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