If all pledges made at the December, 2015 Paris climate agreement (COP21) to curb greenhouse gases are carried out to the end of the century, then risks still remain for staple crops in major “breadbasket” regions and water supplies upon which most of the world’s population depend. That’s the conclusion of researchers at the MIT Joint Program on the Science and Policy of Global Change in the program’s signature publication, the 2016 Food, Water, Energy and Climate Outlook, now expanded to address global agricultural and water resource challenges.

Recognizing that national commitments made in Paris to reduce greenhouse gas emissions fall far short of COP21’s overarching climate target—to limit the rise, since preindustrial times, in the Earth’s mean surface temperature to two degrees Celsius by 2100—the report advances a set of emissions scenarios that are consistent with achieving that goal.

According to the authors, meeting the 2°C target will require “drastic changes in the global energy mix.” To explore what those changes might entail, MIT Joint Program researchers and contributors from the MIT Energy Initiative and the Energy Innovation Reform Project identify current roadblocks to commercializing key energy technologies and systems, and the breakthroughs needed to make them technically and economically viable.

To project the global environmental impacts of COP21 and model emissions scenarios consistent with the 2°C target, the 2016 Outlook researchers used the MIT Joint Program’s Integrated Global Systems Modeling (IGSM) framework, a linked set of computer models designed to simulate the global environmental changes that arise due to human causes, and the latest U.N. estimates of the world’s population.

Key findings in the 2016 Outlook

COP21 Implications

Energy, Emissions & Climate
On the assumption that Paris pledges are met and retained in the post‑2030 period, future emissions growth will come from the Other G20 and developing countries, accelerating changes in temperatures, precipitation, land use, sea‑level rise and ocean acidification.

• Global emissions rise to 64 Gt carbon dioxide‑equivalent (CO₂‑eq) emissions by 2050 and 78 Gt by 2100 (a 63% increase in emissions relative to 2010).
• Energy from fossil fuels continues to account for about 75% of global primary energy by 2050, despite rapid growth in renewables and nuclear, in part due to natural gas.
• The global mean surface temperature increase is in the range of 1.9–2.6°C by 2050 relative to the preindustrial level (3.1–5.2°C by 2100).
• The global mean precipitation increase ranges from 3.9–5.3% by 2050 relative to the preindustrial level (7.1–11.4% by 2100).
• Thermal expansion and land glacier melting contribute 0.15–0.23 meters to sea‑level rise from the preindustrial level by 2050 (0.3–0.48 meters by 2100).

Agriculture

• Our models project mostly positive impacts on crop yields through the end of the century in the regions considered. Projected yields increase from between 0.02 t/Ha–0.75 t/Ha for maize in the U.S.; 0.03 t/Ha–0.9 t/Ha for rice in Southeast Asia; –0.07 t/Ha–0.74 t/Ha for soybean in Brazil; and 0.1 t/Ha–0.8 t/Ha for wheat in Europe.
• For maize (U.S.) and wheat (Europe), we find larger increases in yields in the northern parts of the regions. Production of these crops may shift northward under these conditions.
• For soybean (Brazil) and rice (Southeast Asia), conclusions are less clear, but an overall beneficial effect of climate change on rice is projected in Southern China.
• A large share of the beneficial impact of climate change is attributed to increases in CO₂ concentrations, which improve crop water‑use efficiency and crop productivity. Without CO₂ effects, crop yields are reduced by 8% (maize) to 33% (rice). The quality of cereals, in terms of proteins and other nutrients, may also be reduced.
• Extreme heat and drought linked to a changing climate are likely to increase the frequency of major crop failures. The strong gradient of yield changes across regions could create dislocation and relocation adjustment costs.

Water

• A water stress index shows increased water stress in most regions, resulting from increasing demand due to population activity, economic activity, and changes in climate.
• In many developing countries, demand growth is a bigger source of increasing water stress than changes in climate, but climate change may exacerbate that stress.
• Water demand growth is less of a factor in developed regions, where it has slowed or peaked.
• In some basins, increased water stress is driven by irrigation demand and other water withdrawals. In others, it is driven by decreased runoff due to decreased precipitation. In some regions, increased precipitation and runoff are enough to compensate for increased water demand.
• The largest relative water stress increase is found in Africa, largely driven by increases in population and economic output.
• Approximately 1.5 billion additional people will experience stressed water conditions worldwide by 2050.
• Uncertainty in the climate change pattern plays a role in both where people will face water stress and what level of water stress they will face.

Meeting 2°C and Energy Technologies

• The emissions path under COP21 will result in atmospheric greenhouse gas levels that far exceed those consistent with the 2°C goal. How much we need to do immediately depends on the availability of low‑cost, low‑carbon options in the future.
• If nothing beyond the COP21 proposals is implemented, with high climate sensitivity, the 2°C target may be exceeded in as little as 15 to 20 years from now. Even with low climate sensitivity, on this path, the 2°C target will be passed shortly after midcentury.
• Meeting 2°C requires drastic changes in the global energy mix. Depending on the relative costs of technologies, different technologies could dominate in order to meet a 2°C target.
• Depending on technological advances, the regulatory environment and public acceptance, a variety of different energy technologies could play a dominant role. A portfolio of research and development is needed because we cannot predict which technologies may prove most successful.