- Humans are likely responsible for 93 - 123% of Earth’s net global warming after 1950, says a blockbuster climate report issued on Friday. The Climate Science Special Report is the first product released by the Fourth National Climate Assessment (NCA); the core assessment itself, focusing on impacts, will be released in 2018. The NCA is a congressionally mandated quadrennial effort by hundreds of U.S. scientists to assess how the climate is changing in the United States. The project is carried out by the U.S. Global Change Research Program. Preparation of the report included workshops around the nation, a public-comment period on the draft, and a technical review spanning 13 agencies.
- Warmest in more than a thousand years. A major paleoclimate study has shown that for each of the world’s seven major continental regions, the average temperature for 1971-2000 was the highest in more than 1300 years. There is significant uncertainty around these estimates, but a separate study found that temperate North America as a whole (including most of the contiguous U.S.) is having its warmest 30-year periods in at least 1500 years.
- It’s going to get a lot warmer in the coming decades. Temperatures across the contiguous U.S. have risen about 1.8°F (1.0°C) over the period 1901-2016. “Surface and satellite data are consistent in their depiction of rapid warming since 1979,” the report notes. By the period 2070-2100 (when today’s infants will be elders), U.S. temperatures may be 2.8 to 7.3°F warmer than the 1976-2005 average if greenhouse-gas emissions are reined in strongly—or 5.8 to 11.9°F warmer if emissions continue to grow at the pace of recent decades.
- It’s getting wetter, but not everywhere. Average precipitation for the nation as a whole has increased by about 4% since 1901. This is mainly due to large increases in autumn (see Figure 4). Overall, precipitation has decreased over much of the West, Southwest, and Southeast, and increased over most of the Great Plains, Midwest, and Northeast.
- The biggest precipitation events are getting bigger. Between 1901 and 2016, the amount of moisture one would get on the wettest day across a five-year period has increased by anywhere from 1% in the Southwest to 27% in the Northeast. The jumps are even larger for the period 1958 – 2016, when considering the amount of moisture falling in the top 1% of all wet days: from a 9% increase in the Northwest to 55% in the Northeast (although Hawaii and the Caribbean saw drops of 11% and 12%, respectively).
- Wetter north, drier south? Winter and spring are projected to get wetter on average in the northern U.S., including Alaska. However, parts of the Southwest may see a decrease in winter and spring moisture. As the century rolls on, we’re likely to see a continued increase in the frequency and intensity of heavy precipitation events (see Figure 4 below).
- The impacts of sea level rise are not limited to future decades—they’re happening right in front of us, right now. “Nuisance” flooding has become a growing problem in places ranging from Miami Beach to San Francisco. In Maryland, both Annapolis and Baltimore now get more than nine times the number of flood days they experienced in the 1960s.
Figure 1. (left) Global annual average temperature has increased by more than 1.2°F (0.7°C) for the period 1986–2016 relative to 1901–1960. Red bars show temperatures that were above the 1901–1960 average, and blue bars indicate temperatures below the average. (right) Surface temperature change (in °F) for the period 1986–2016 relative to 1901–1960. Gray indicates missing data. Image credit: Figures 1.2. and 1.3 of Chapter 1, Climate Science Special Report.
The information contained in this post was gathered from a blog post from Dr. Jeff Masters.