Today, the US Global Climate Change Research Program released the Climate Science Special Report, Vol. 1 of the Fourth National Climate Assessment mandated by Congress to provide the latest scientific basis and impacts from climate change on the United States. Climate science continues to evolve, but in the direction of more significant realization of how humans have influenced the climate thus far, as well as how much more influence will come in the not to distant future.
Below are some of the headline findings provided in the rather powerful report (be prepared for a lot of INTENSE info):
- Earth’s average temperature has increased by 1 degree C (1.8 F) during the 1901-2016 period. This is faster than any rate known in the last 1,700 years.
- The average temperature of the contiguous United States has also increased by 1 degree C (1.8 F) during the 1901-2016 period. Satellite and surface observations are consistent in the detection of this rapid rise in temperature. With no change in the rate of greenhouse gas emissions, the CONUS is expected to experience a more abrupt average rise in temperature of 3.2-6.6 degrees C (5.8-11.9 F) between now and 2100.
- Temperature extremes in the United States are trending significantly toward record high temperatures over record low temperatures. This trend is expected to continue with the number of below freezing days also continuing to decline and days above 32 degrees C (90 F) continuing to rise.
- The global influence of natural variability is limited to small fraction of observed climate trends. Solar output and the Earth’s internal natural variability have contributed only marginally to the observed changes in the climate system over the past century. There is no convincing evidence for natural cycles in the observational record that could explain the changes in the climate system.
- Heavy precipitation events have increased across the US since 1901. The highest increase over the Northeast and the second highest increase over the Midwest.
- Northern Hemisphere spring snow cover, North American maximum snow depth and Western US snow-liquid equivalent have all declined since the early 20th century. At current rates of decline and assuming no change in water resource management, chronic, long-duration hydrological drought conditions are possible for portions of the United States by 2100.
- Global mean sea-level has risen 7-8 inches (~0.2 m) since 1900 with 3 of those inches since 1993. Relative to the year 2000 is very likely global mean sea-levels will rise up to 0.6 ft (0.18 m) by 2030, 1.2 ft (0.38 m) by 2050 and 4.3 ft (1.3 m)+ by 2100. A more rapid degradation of the West Antarctic Ice Sheet may mean physically possible sea level rise theoretically exceeding 8 ft (2.4 m) by 2100 (confidence is low on this).
- The global ocean has absorbed more than 93% of the heat caused by global warming since the mid-20th century. The oceans have warmed by about 0.7 degrees C (1.3 F) during the 1900-2016 period. Assuming no emissions changes, warming of the oceans by an average of 2.7 degrees C (4.9 F) is expected by 2100.
- The global ocean continues to undergo rapid acidification because of dissolved carbon dioxide from atmospheric emissions. The rate of acidification is unparalleled in the past 66 million years (since the Cretaceous-Paleogene Impact Event). At the current rate, the pH of the global ocean may decline from its current average of 8.1 to as low as 7.8 by the end of the century. Seawater with pH <8 can be corrosive to shellfish, plankton and coral which depend on carbonate structures for their shells, backbones and skeletons. The greatest change in acidity will be in Arctic Ocean.
- The Arctic is warming at a rate approximately twice as fast as the global average with a rapid decline in sea ice volume and extent since satellite observations began in 1979. At the current rate of warming, the Arctic Ocean will be effectively ice-free in the month of September by the 2040s.
- Global warming has contributed “significantly” to ocean-atmosphere variability in the North Atlantic Ocean; as a result these changes have contributed to the observed upward trend in North Atlantic hurricane activity since the 1970s. North Atlantic hurricanes are expected to increase in intensity (maximum sustained wind potential) with increasing precipitation rates during the 21st century.
- Large forest fires in the Contiguous US and Alaska have increased since the early-1980s. This increase is expected to continue with “profound” impacts on ecosystems.
Some other findings of note:
-For the period 1901-2016, the Dust Bowl Era (mid-1930s) remains the most extreme era for heat. This is thought to be largely the result of significant land-surface feedbacks caused by precipitation deficits and poor land management leading to reduced vegetation and strong surface heating (which in turn promoted further drying and land degradation). However, we are on a path to eclipse this period in US climate history in the coming decades, particularly as colder conditions (more found in 1930s winters for example) continue to decline in a warming climate and extreme heat continues to increase.
-The Climate report explains (as has been explained in previous scientific literature) the period of so-called “global cooling” which occurred from the mid-1940s to mid-1960s: aerosol particles generated by WWII and post-war industrial production (esp. coal power plants) which reflected some solar radiation into space temporarily slowing long-term global warming, even as carbon dioxide concentration in the atmosphere continued to increase.
-The report notes that annual precipitation has decreased over the West, Southwest and Southeast, while increases have occurred over the Plains, Midwest and Northeast. They specifically mention an increase in mesoscale convective systems (organized clusters of thunderstorms which dump significant rainfall) over the Plains and Midwest since 1979. Mesoscale convective systems are expected to increase in frequency and intensity during the 21st century.
-While tornado climatology related to climate change has been difficult to understand because of the reliability of storm reports before the 1990s, scientists involved in the report have concluded one interesting aspect…there is moderate confidence in a decrease in tornado days (day when tornadoes of any number are confirmed), as tornadoes are increasing on those days. Greater volatility in tornado occurrence year-to-year as well as a trend toward an earlier first occurrence during the year have been observed. Studies looking at the ingredients for severe storms with all modes of potential activity (tornadoes, hail, wind) suggest an increased frequency and intensity of severe storms over areas prone to them in the US in a warmer world, but confidence on details is low.
-This report concluded that observed drought and precipitation increases (1901-2016) cannot be confidently attributed human-induced global warming. The Dust Bowl Era remains the benchmark period for extreme drought conditions. However recent negative trends in soil moisture are believed to be attributable to warming temperatures. Although soil moisture projections in climate models are still considered in their “elementary” stages in the science, based on what is known, there appears to be a signal for further decreases in soil moisture over portions of the US (particularly West and Plains) by the end of this century, increasing the risk of chronic hydrological drought.
-I find the key finding #11 I listed particularly important. There has been much debate between scientists (particularly more observational minded meteorologists vs. climatologists) about whether there has been truly observable increase in N. Atlantic hurricane activity seasonally beyond the natural variability, given the limited period of reliable satellite record and intensity measurements. This statement is given MODERATE confidence given that global warming has caused increases in sea-surface temperatures, oceanic heat content and natural cycles on multi-annual and multidecadal time scales involve changes in not only these thermodynamic variables but also dynamic ones in response (vertical wind shear, position/intensity of monsoon troughs, development of tropical waves into organized TCs).
Climate change will likely be one of the most difficult challenges the world will face this century (at least). Why? Why should we care?
When it comes to effects on people (which is what people care about), at the end of the day, what matters for the livelihood of people rich or poor? Food, water, living space. If these become challenged, you get human suffering (from economic to health threats) and geopolitical problems. The potential for significant drying and increasing chronic hydrologic droughts from loss of snowpack will lead to increasing populations in demand for resources seriously straining water resources. Crops around the world will face increasing difficulties from heat stress, prolonged droughts mixed with periods of more intense heavy rainfall events. Acidification and warming may threaten marine food resources already strained by overfishing around the world. Living space will become slowly threatened by sea level rise in low-lying areas and island nations…and more readily in the coming decades…by repeated far more extreme heat waves than previously in already hot, humid environments where cooling is not readily available, and possibly by diseases as ecosystems shift to different places, along with pests (which will also impact crops potentially).
Climate change isn’t just about warming, it’s about cascading impacts on the whole of the climate system. Without a drastic global shift to a low-carbon energy sources and the advancement of technology to remove carbon dioxide from the atmosphere, we are in store for a very challenging period in human history. This isn’t worse-case/best case or any of this. This is simply the path that we are on, no over-dramatic statements nor downplaying needed or tolerated. Hopefully we via our governments make the right choices.
–Meteorologist Nick Humphrey