The world is fast approaching 1.5 Celsius, the limit scientists set to avoid the worst impacts of climate change. What does reaching that limit mean for the planet and its denizens?
A world that hits the 1.5 C mark is one where people suffer from extreme weather events, including severe heat waves. According to the World Resources Institute, with 1.5 C warming, nearly 14 percent of the global population would be exposed to intense heat waves at least once every five years. Around nine percent of the global population will experience extreme heat waves at least once every 20 years.
Increased runoff and floods will occur in some regions. There will likely be a sea-ice-free summer every 100 years. Sea level will rise by 1.3 feet (0.4 meters) in 2100, compared to 1986 to 2005 levels. By 2100, up to 69 million people could experience flooding.
The risk of drought increases. One model found that drought probability triples in Brazil and China, nearly doubles in Ethiopia and Ghana, substantially increases in Egypt, and increases slightly in India. Drought impacts crop yields. One study looked at five climate models and found that global maize yields declined somewhat under a 1.5 C scenario and by 10.8 percent under a 2 C scenario.
Ecosystems will change with increased warming. With 1.5 C of warming, biome shifts, such as tundra becoming forest, are projected to cover four percent of the earth’s land areas. Under 2 C warming, the risk increases to 13 percent. Increased warming puts permafrost at a greater risk of melting. With 1.5 C of warming, 21 to 37 percent of total Arctic permafrost would melt, and with 2 C warming, thawing permafrost increases to 34 to 47 percent.
California’s Central Valley: A Model for Agricultural Impacts
California’s Central Valley, a big swath of the state’s interior, includes the Sacramento and San Joaquin Valleys. The area produces a third of the nation’s vegetables, two-thirds of its fruits and nuts, and all of its almonds and raisins. Climate models project that the mean annual temperature will increase by five to six degrees this century. The length of hot temperatures will increase from two months to four months.
During the next few decades, models project an average temperature rise of one to 2.3 degrees F. The number, length, and intensity of heat waves will significantly rise. Every year in the last quarter of the century will have one or more five-day periods with temperatures above today’s threshold considered extreme for the area. Farmworkers harvest the Valley’s crops, and extreme heat poses a risk to them.
Rainfall will vary widely from year to year. Some models predict California will be 15 to 35 percent drier by 2100. There will likely be an increase in summer dryness even in years of higher-than-average precipitation. There may be more years with many atmospheric river events, as there was this earlier this year. Those AR events caused many acres of farmland in Kings County to flood. The length of AR events is predicted to increase, which may result in more frequent and severe floods.
California agriculture depends on irrigation. Models predict that water demand by plants not met by soil moisture will increase. Beyond 2030, the 10-year average will exceed the historical extreme. There will be eight percent more critically dry water years during the latter half of this century than in 1951 to 2000 in the Sacramento Valley and 32 percent more in the San Joaquin Valley.
All this portends a headlong drive toward 1.5 C unless we immediately slow down and alter course.
