Global warming is irreversible, U.S. study concludes

Washington, D.C. – The U.S. Climate Change Science Program, a research project led by the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Department of Commerce, has published a new dramatic report on global climate change and the impact in the United States. It is the most dramatic report published by the U.S. government so far, indicating that the pace of global warming can be slowed, but not stopped or reversed. The advice is to better adjust to the effects of global warming.

“No matter how aggressively heat-trapping emissions are reduced, the world will still experience some continued climate change and resulting impacts,” the conclusion of the report (13 MB PDF file) states.

The scientists believe that some of the gases that are emitted today are long-lived and lead to circumstances that create high enough levels of atmospheric heat-trapping gases for hundreds of years. Additionally, the world’s oceans already have absorbed much of the heat added to the climate system and it is expected that they will retain that heat and in fact support the global warming process “for many decades,” even if mankind is able to reduce human-induced emissions. And, of course, there are natural causes of greenhouse gas emissions, such as eruptions of volcanoes, as well as effects of climate change that may push us beyond certain thresholds of additional climate change that could create a virtually unstoppable chain reaction of ecological changes that would lead to further climate changes.

The agency outlines such expected changes in a different report entitled “Thresholds of Climate Change in Ecosystems”: For example, predicted warmer, drier conditions in the semiarid forests and woodlands of the southwestern United States would place those forests under more frequent water stress, resulting in the potential for shifts between vegetation types and distributions, and could trigger rapid, extensive, and dramatic forest dieback.

Alaska is often described as a key example of observed climate-related threshold change. Warming has caused a number of effects, including earlier snowmelt in the spring, reductions in sea-ice coverage, warming of permafrost, and resultant impacts to ecosystems including dramatic changes to wetlands, tundra, fisheries, and forests, including increases in the frequency and spatial extent of insect outbreaks and wildfire, scientists for the U.S. Climate Change Science Program said.  

Observations indicate that the global average temperature since 1900 has risen by about 1.5° F. By 2100, it is projected to rise another 2 to 10°F, according to the report. And while temperatures in the U.S. have risen in line with the rest of the world, scientists now believe that temperatures in the U.S. are “very likely” to rise much faster than the global average down the road. “Increases at the lower end of this range are more likely if global heat-trapping gas emissions are cut substantially, and at the upper end if emissions continue to rise at or near current rates,” the report states. Human influence on the climate system is believed to remain the key factor that affects the range of temperature changes.

While the report states that it is imperative that emissions of carbon dioxide is imperative, it also says that reducing emissions of the greenhouse gas would only “reduce” warming over this “century and beyond”. As a result we will have to adapt to inevitable changes, which will “impact human health, water supply, agriculture, coastal areas, and many other aspects of society and the natural environment.” Additional expected changes include “more intense hurricanes and related increases in wind, rain, and storm surges (but not necessarily an increase in the number of storms that make landfall), as well as drier conditions in the Southwest and Caribbean.”

The report does not recommend specific actions to respond to climate change, but is limited to general reactions. The first is “mitigation”, which would reduce the effects of global warming. The second is “adaptation,” which would help humans to better respond to climatic conditions. 

Mitigation and adaptation are both essential parts of a climate change response strategy, says the report, adding that effective mitigation reduces the need for adaptation. The scientists admit that there are limits to how much adaptation can be achieved, but say there are encouraging elements here too:

“Adaptation involves deliberately adjusting to observed or anticipated changes to avoid or reduce detrimental impacts or to take advantage of beneficial ones. For example, a farmer might switch to growing a different crop variety better suited to warmer or drier conditions. A company might relocate key business centers away from coastal areas vulnerable to sea-level rise and hurricanes.”