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MIT Report Charts Likely Global Environmental Changes in the 21st Century

In 2015 the Paris Agreement specified the need for its nearly 200 signatory nations to implement greenhouse gas emissions reduction policies consistent with keeping the increase in the global average temperature since preindustrial times to well below 2 degrees Celsius — and pursue efforts to further limit that increase to 1.5 C.

Recognizing that the initial, near-term Paris pledges, known as Nationally Determined Contributions (NDCs), are inadequate by themselves to put the globe on track to achieve those goals and thus avoid the worst consequences of climate change, the agreement calls for participating nations to strengthen their NDCs over time. Toward that end, the Intergovernmental Panel on Climate Change (IPCC) released a special report on Oct. 8 on pathways to achieving the 1.5 C goal, and the next Conference of the Parties (COP24) to the United Nations Framework Convention on Climate Change (UNFCCC) convenes in December.

In line with these developments, the MIT Joint Program on the Science and Policy of Global Change has released its 2018 Food, Water, Energy and Climate Outlook. Based on a rigorous, integrated analysis of population and economic growth, technological change, Paris Agreement NDCs, and other factors, the MIT report projects likely global and regional environmental changes over the course of this century and identifies steps needed to align near-term Paris pledges with the long-term 2 C and 1.5 C goals.

This year's Outlook extends the program's analysis of Paris Agreement pledges to include commitments of most of the countries of the world, uses a newly updated version of the Joint Program's Integrated Global System Modeling (IGSM) framework, and relies on updated gross national product (GDP) projections. Projections of the Outlook, which assume that all NDCs (generally including commitments only through 2025 or 2030) are met and retained throughout the century, map out the future of energy and land use; water and agriculture; and emissions and climate. The Outlook concludes with expert perspectives on the progress of key countries and regions in fulfilling their short-term Paris pledges, and potential pathways to meeting the long-term Paris goals.

Future of energy, water and food

Between 2015 and 2050, population and economic growth are projected to lead to further increases in primary energy of about 33 percent, growth in the global vehicle stock by nearly 61 percent, further electrification of the economy, and, with continued land productivity improvement, relatively modest changes in land use.

While successful achievement of Paris Agreement pledges should accelerate a shift away from fossil fuels (from 84 percent in 2015 to 78 percent of primary energy use by 2050)  and temper potential rises in fossil fuel prices, it is likely to contribute to increasing global average electricity prices (rising to about 31 percent above 2015 levels by 2050).

Water and agriculture are key sectors that will be shaped not only by increasing demands from population and economic growth but also by the changing global environment. Climate change is likely to add to water stress and reduce agricultural productivity, but adaptation and agricultural development offer opportunities to overcome these challenges.

Projections for the U.S. show a central tendency of increases in water stress between 2015 and 2050 for much of eastern half of the country and the far west, and a slight reduction in water stress for the upper plains and lower western mountains.

Projections for agricultural production and prices reflect the effects of the Paris Agreement on energy and land-use decisions. Results show that at the global level between 2015 and 2050, the value of overall food production increases by about 130 percent, crop production increases by 75 percent and livestock production by 120 percent. Simulating yield effects of climate change ranging from reductions of approximately 5 percent to about 25 percent varying by crop, livestock type, and region drawn from studies reviewed by the IPCC, the Outlook finds that commodity prices increase above the baseline projection by about 4-7 percent by 2050 for major crops, 25-30 percent for livestock and forestry products, and less than 5 percent for other crops and food.  

Emissions and climate projections

Total global emissions of greenhouse gases remain essentially unchanged through 2030, but gradually increase thereafter (rising by about 33 percent between 2015 and 2100) as regions of the world that have not adopted absolute emissions constraints see emissions increases. Future emissions growth will increase the risks associated with global environmental change.

The projected median increase in global mean surface temperature by 2100, above the 1861-1880 mean value, is 3.0 C (the 10 and 90 percent confidence limits of the distribution are 2.6 and 3.5 C). Other important projected changes in the Earth system include: a median ocean pH drop to 7.85 from a preindustrial level of 8.14 in 1861 and, relative to 1861-1880 mean values, a median global precipitation increase of 0.18 millimeters per day and median sea-level rise of 0.23 meters in 2100. The latter figure, based solely on thermal expansion, will likely be higher due to contributions from melting glaciers and ice sheets.

Prospects for meeting near- and long-term Paris goals

The MIT Joint Program invited leading experts on policy developments around the world to provide their perspectives on how well key countries and regions are progressing in fulfilling their NDCs. They report on some bright prospects, including expectations that China may exceed its commitments and that India is on a course to meet its goals. But they also observe a number of dark clouds, from U.S. climate policy developments to the increasing likelihood that financing to assist the least developed countries in sustainable development will not be forthcoming at the levels needed.

Looking at the long-term, the 2018 Outlook finds that the Paris Agreement's ambitious targets of keeping global warming well below 2 C and ideally below 1.5 C remain technically achievable, but require much deeper, more near-term reductions than those embodied in current NDCs. Making deeper cuts immediately (2020) rather than as a next step in the Paris process (waiting until 2030) would lower the carbon prices needed to achieve long-term goals, and lessen the need for unproven options to achieve zero or negative emissions after 2050.

"More aggressive action sooner rather than later on mitigation will give us a better chance of meeting the long-term targets," says MIT Joint Program co-director John Reilly. "At the same time, we need to prepare our homes, communities and the industries on which we depend for the climate change we will experience, even if we manage to hold the increase to less than 2 or 1.5 degrees, and make even greater preparations to account for the risk that we may fail to hold the line on the temperature rise."

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