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July 2017, Volume 23, Number 3

Climate Change

President Trump on June 1, 2017 announced that the US would withdraw from the 2015 Paris climate agreement and negotiate a better deal to prevent the world's average temperature from increasing by two degrees Celsius above pre-industrial levels. Restricting the increase in temperature to two degrees requires a reduction in carbon dioxide emissions of 6,000 gigatons.

Trump fulfilled a campaign promise despite opinion polls showing that most Americans support international efforts to reduce global warming. Trump took particular aim at the Green Climate Fund, a $100 billion-a-year transfer from rich to poor nations to help them to cope with global warming.

Under the Paris agreement, the Obama administration pledged to cut US greenhouse gas emissions 26 to 28 percent below 2005 levels by 2025 and to provide $3 billion to the Green Climate Fund by 2020. Polls find that most Americans believe the world is warming and that human activities are a major reason for this warming, but actions to limit global warming are rarely at the top of voter concerns.

Many world leaders expressed disappointment at Trump's withdrawal decision. Leaders of major EU countries, China and India said they remain committed to reducing greenhouse gas emissions as called for in the Paris agreement.

China is currently the largest single carbon emitter, emitting about twice as much carbon as the US, but the US emits more per capita and has emitted a third of the excess carbon in the atmosphere that is warming the planet. The EU's 28 member states are also responsible for a third of the excess carbon emissions that have accumulated; the EU has pledged to reduce carbon emissions by 40 percent from 1990 levels by 2030.

Some say US withdrawal was unnecessary. Article 4.11 of the Paris agreement says that a nation "may at any time adjust its existing nationally determined contribution with a view to enhancing its level of ambition," which means the US could adjust its greenhouse gas emissions upward or downward while remaining in the agreement.

Fossil fuels today provide over 80 percent of global energy needs; wind and solar provide less than one percent. A major policy issue is how much to subsidize renewable energy development to speed the transition away from fossil fuels, and whether more expensive renewable energy will slow economic growth.

Stanford's Mark Z. Jacobson argues that the US could obtain all its energy from renewables by 2050 by expanding hydropower and storing energy from the sun and wind. Jacobson says that if the US stored almost two months of its energy needs, renewables would be reliable, even though today the ten largest energy storage systems store less than an hour's US energy needs.

Critics question Jacobson's assumptions, including an easy transition to hydrogen-powered planes, factories closing when sun and wind power are not available, and a very low cost of capital. Jacobson assumes that the US could add the equivalent of 600 Hoover dams to provide 1,300 gigawatts of hydropower, which would mean many more dams.

Most of the world's fresh water stored as ice is in Antarctica, but some of the fastest-melting ice is in Greenland. By some estimates, the world's oceans would rise over 20 feet if all of Greenland's ice melted. Greenland loses about 200 gigatons (a billion metric tons) of ice each year via calving glaciers. In 2012, the rate of calving increased sharply, but in 2017 the accumulation of ice reached record levels.

Project Midas in June 2017 reported that one of the largest icebergs ever recorded, Larsen C at almost 2,000 square miles or about the size of Delaware, was poised to break off of the northwestern portion of Antarctica. The ice of Antarctica averages over a mile thick, and accelerated melting of Antarctica's ice is expected to raise sea levels.

Australia's Liberal (conservative) government in 2016 appointed a director of its science research agency who favored applied over basic science, including on the effects of global warming. The Liberal government won re-election in summer 2016 elections but with a diminished majority, prompting the naming of a new science director.