National Climate Assessment

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U.S. Global Change Research Program. Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. Washington, DC, 2018.

Federal law requires the government to issue a new climate assessment every four years. Thirteen government agencies participated in the current assessment, including the Departments of State, Commerce, Interior, Transportation, Health and Human Services, Defense, Agriculture, and Energy; along with the National Science Foundation, Smithsonian Institution, U.S. Agency for International Development, National Aeronautics and Space Administration, and Environmental Protection Agency.

This year’s report is Volume II of the fourth National Climate Assessment. Volume I, issued last year, provided a comprehensive summary of climate changes themselves, based on the best science available. Findings from Volume I are incorporated into the impact assessment in Volume II.

Full disclosure: I haven’t read all 1,656 pages of this report. What I am summarizing is the 40-page overview in Chapter 1, supplemented by a brief look at selected other chapters.

Here is a statement of the report’s general conclusions:

This report draws a direct connection between the warming atmosphere and the resulting changes that affect Americans’ lives, communities, and livelihoods, now and in the future….It concludes that the evidence of human-caused climate change is overwhelming and continues to strengthen, that the impacts of climate change are intensifying across the country, and that climate-related threats to Americans’ physical, social, and economic well-being are rising.

The climate changes

The most obvious change is that the country is getting warmer along with the rest of the planet. On the average, temperatures have increased by 1.8 degrees Fahrenheit across the contiguous United States since around 1900. The warming in Alaska has been even greater. Since the 1980s, arctic sea ice has been decreasing by 11-16% per decade. (Here in the Southeast, the rise in temperature is expected to be smaller than in most of the northern United States, and the main effect will be warmer nights rather than hotter days.)

The median sea level along our coasts has risen about 9 inches since the early 20th century, due to ocean warming and melting land ice. The oceans have also become more acidic as they have absorbed more carbon dioxide.

Although these changes may sound small, they are enough to produce large changes in the weather. Extreme climate-related weather events are becoming more common, and when they occur they often last longer and cause more damage. We are experiencing more frequent and longer heat waves, especially in urban areas. More of our annual rainfall is coming in the form of intense, one-day rainfalls that cause more flooding, especially in coastal areas affected by higher sea levels and tides. Recent hurricanes have been especially severe. Hot, dry conditions have contributed to unusually large wildfires in the western states.

Scientists have known for a long time that naturally occurring greenhouse gases in the atmosphere trap some of the heat radiating from the Earth’s surface. That keeps the planet surface warm enough to be habitable for living things. But in the industrial era, human activity has added dramatically to these gases, especially through emissions of carbon dioxide.  Carbon dioxide in the atmosphere has increased by about 40%. Burning fossil fuels accounts for about 85% of all greenhouse gas emissions by humans.

Scientists have concluded that non-human factors alone cannot account for climate change. In fact, “Without human activities, the influence of natural factors alone would actually have had a slight cooling effect on global climate over the last 50 years.” Scientists have found no credible alternative to the consensus view that human activity, especially the burning of fossil fuels, is responsible for global warming.

Scenarios for future change

Science is often in the position of being unable to predict the future with certainty, but being able to project possible futures based on reasonable assumptions. For example, financial planners cannot predict a couple’s future retirement income without making assumptions about how much they will save, how they will invest it, and how closely market performance will conform to historical averages. So they often construct multiple scenarios based on a reasonable range of assumptions.

Climate scientists do not know how much global temperatures will increase or how much sea levels will rise, mainly because they don’t know how much humans will curb their emissions of greenhouse gases. So the National Climate Assessment relies on a “suite of possible scenarios” based on “Representative Concentration Pathways”–that is, different concentrations of carbon dioxide in the atmosphere later this century.

Some additional rise in temperature is inevitable over the next few decades, even if we start reducing carbon emissions now. That’s because the climate system responds slowly to changes in greenhouse gas levels. Even in the lowest scenario considered, “additional increases in temperatures across the contiguous United States of at least 2.3ºF (1.3ºC) relative to 1986-2015 are expected by the middle of this century.” Around mid-century, the various scenarios diverge dramatically. In a “very low” scenario, which assumes that emissions are peaking now, temperatures level off after 2050. In a “low” scenario, which assumes that emissions peak around 2050, temperatures rise another 2.3-6.7ºF (1.3-3.7ºC) by the end of the century. In a “higher” scenario, which assumes that emissions keep rising, temperatures rise another 5.4-11.0ºF (3.0-6.1ºC) by the end of the century, resulting in the most catastrophic effects. “Coastal flood heights that today cause major damages to infrastructure would become common during high tides nationwide.”

Perhaps the most sobering finding is that current global trends in annual greenhouse gas emissions are most consistent with the highest scenario considered. The evidence so far does not inspire confidence that global emissions are peaking now or will do so in the near future. But business as usual is not a viable option, and serious emission reductions are required soon to avoid catastrophic outcomes before the end of the century.

This is probably what the White House was referring to when it dismissed the report as being “largely based on the most extreme scenario,” as if the researchers deliberately chose the most pessimistic assessment in order to upset people. What they actually did was project a reasonable range of scenarios, but then come to the scientific conclusion that allowing carbon emissions to rise would result in the least desirable outcome. What the Trump administration is doing is rejecting the report as too dire, and then insisting on continuing the policies that are most likely to produce the most dire results!

The risks

The report discusses three kinds of risks arising from climate change: risks to economy and infrastructure, risks to the natural environment and “ecosystem services,” and risks to human health and well-being.

Climate change could cause substantial damage to infrastructure and private property. Regional economies and industries that depend on favorable climate conditions, such as agriculture, tourism and fisheries, will be especially vulnerable. The researchers tried to quantify many of these effects throughout the report, but the overview included only a few general references to dollar amounts: “The potential for losses in some sectors could reach hundreds of billions of dollars per year by the end of this century.”

Climate change produces economic losses in many different ways. Extreme heat waves and more powerful storms put stress on energy systems and create widespread power outages. Much of the infrastructure for producing energy is located along ocean and gulf coasts that are vulnerable to strong hurricanes and increased flooding. Although the warming climate lengthens the growing season, yields for many major crops are expected to decline because of excessive heat and greater pest activity. Bad weather around the world also impacts on the U.S. economy by disrupting international supply chains, as happened with hard-drive imports from Thailand in 2011.

An example of what the report calls “ecosystem services” is the availability of water or snow for drinking and recreation. In the Southwest, “intensifying droughts, heavier downpours, and reduced snowpack are combining with other stressors such as groundwater depletion to reduce the future reliability of water supplies in the region.”

Heat waves are associated with higher death rates, especially for older adults, pregnant women, and children. Climate change will also increase exposure to pollen allergens associated with allergic illnesses such as asthma and hay fever. And as North America warms, disease-carrying insects from Southern climates are migrating northward.

Since low-income communities are especially vulnerable to many of these risks, “climate change threatens to exacerbate existing social and economic inequalities….”

Reducing the risks

Many states, cities and businesses have taken some measures to reduce greenhouse gas emissions or to adapt to climate changes. However, the report states that “these efforts do not yet approach the scale needed to avoid substantial damages to the economy, environment, and human health expected over the coming decades.” Time is of the essence, since some effects of climate change will be difficult or impossible to reverse if they are allowed to occur. Once ice sheets melt enough to make sea levels higher and coastal cities uninhabitable, those conditions may persist for thousands of years.

The report makes a distinction between mitigation, which reduces risks by limiting further climate change, and adaptation, which reduces risks by softening the impact of the climate changes that do occur.

With regard to mitigation, one area where some progress has been made is the power sector of the economy. Greenhouse gas emissions from power generation dropped 25% from 2005 to 2016, the greatest decline for any sector. As a result, the sector with the largest emissions is now transportation.

Last week’s announcement of automobile plant closings by GM is very much related to our emissions problems. By increasing domestic gasoline production, we have lowered the price of gas, but that encourages consumers to buy larger, less fuel-efficient vehicles. The plants to be closed are producing smaller, more fuel-efficient cars for which there is currently less demand. Gas prices are artificially low, since they don’t include the ultimate cost to society of environmental damage. A carbon tax would be a rational way of discouraging our short-sighted reliance on fossil fuels, but that requires courageous leadership and a better-informed public.

With regard to adaptation, some communities have taken measures like strengthening buildings to withstand extreme weather events. They tend, however, to prepare only for the range of events that are familiar to them, rather than the even wider range that scientists anticipate. They are more likely to raise construction standards than to block construction altogether in high-risk locations.

In many areas, the costs that can be avoided through advance planning and investment are substantial. For example, “More than half of damages to coastal property are estimated to be avoidable through adaptation measures such as shoreline protection and beach replenishment.” Nevertheless, the researchers believe that moving populations away from the most threatened coastlines will become unavoidable.

Crisis, what crisis?

With the issuance of this report, the American people have just experienced a remarkable spectacle. On the one hand, thirteen federal agencies have collaborated to produce the most scientific report they can assemble on climate change, as mandated by federal law. On the other hand, the Trump administration has tried to bury it by releasing it on Black Friday and encouraging people not to believe it. “Whatever happened to Global Warming?” the president tweeted during a recent cold snap.

The President of the United States has considerable power both to define issues and to address them. This president is doing what he can to ridicule the whole idea of controlling emissions and undermine existing efforts to do so. He has blocked the previous administration’s clean energy initiative, lowered standards for vehicle fuel efficiency, taken the U.S. out of the Paris Agreement, and encouraged more fossil fuel production. I am tempted to use a term like “criminal negligence” to refer to his leadership in this area, except that ignorance is not a crime.

President Trump’s idea of a real crisis is illegal immigration. But according to The Economist, total apprehensions at the border were already way down before he even took office. “Not only have the migration numbers tumbled and the share of Mexicans among them dwindled. More Mexicans are now returning to Mexico than are coming to the United States illegally.” Central American migrants have increased in the past decade, but their numbers are still too small to change the overall story. By trying to close the border to asylum seekers, Trump provokes border confrontations that seem to confirm his largely phony crisis.

Given Donald Trump’s hyper-nationalist worldview and distorted priorities, it’s no wonder that immigration far surpasses climate change as a hot political topic and campaign issue. Too many Americans seem willing to follow this president wherever he leads, even if it’s over a climate-change cliff. Isn’t it time for the country to come to its senses and demand realistic, fact-based leadership?

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