is it true or false that the climate model projections for the 21st century depi
ID: 288982 • Letter: I
Question
is it true or false that the climate model projections for the 21st century depict a much warmer future and there will be a significant reduction in long-term average precipitation for California is it true or false that the climate model projections for the 21st century depict a much warmer future and there will be a significant reduction in long-term average precipitation for California is it true or false that the climate model projections for the 21st century depict a much warmer future and there will be a significant reduction in long-term average precipitation for CaliforniaExplanation / Answer
True
The latest projections, based on state-of-the art climate models, indicate that if global heat-trapping emissions pro- ceed at a medium to high rate, temperatures in California are expected to rise 4.7 to 10.5°F by the end of the century. In contrast, a lower emis- sions rate would keep the projected warming to 3 to 5.6°F. These temperature in- creases would have wide- spread consequences includ- ing substantial loss of snow- pack, increased risk of large wild res, and reductions in the quality and quantity of certain agricultural products. The state’s vital resources and natural landscapes are already under increasing stress due to California’s rapidly growing population, which is ex- pected to grow from 35 million today to 55 million by 2050.
Precipitation
On average, the projections show little change in total annual precipitation in California. Furthermore, among several models, precipitation projections do not show a consistent trend during the next century. The Mediterranean seasonal precipitation pattern is expected to continue, with most precipitation falling during winter from North Paci c storms. One of the three climate models projects slightly wetter winters, and another projects slightly drier winters with a 10 to 20 percent decrease in total annual precipitation. However, even modest changes would have a signicant impact because California ecosystems are conditioned to historical precipitation levels and water resources are nearly fully utilized.
Models described in the IPCC First Assessment Report showed that a warmer mean temperature increases the probability of extreme warm days and decreases the probability of extreme cold days. This result has appeared consistently in a number of more recent different climate model configurations. There is also a decrease in diurnal temperature range (DTR) since the night-time temperature minima warm faster than the daytime maxima in many locations. Although there is some regional variation, some of these changes in DTR have also been seen over a number of areas of the world in observations. In general, the pattern of change in return values for 20-year extreme temperature events from an equilibrium simulation for doubled CO2 with a global atmospheric model coupled to a non- dynamic slab ocean shows moderate increases over oceans and larger increases over land masses. This result from a slab ocean configuration without ocean currents is illustrative and could vary from model to model, though it is similar to results from the fully coupled version in a subsequent study.
The greatest increase in the 20-year return values of daily maximum temperature is found in central and southeast North America, central and south-east Asia and tropical Africa, where there is a decrease in soil moisture content. Large extreme temperature increases are also seen over the dry surface of North Africa. In contrast, the west coast of North America is affected by increased precipitation resulting in moister soil and more moderate increases in extreme temperature. There are small areas of decrease in the Labrador Sea and Southern Ocean that are associated with changes in ocean temperature. The changes in the return values of daily minimum temperature are larger than those of daily maximum temperature over land areas and high latitude oceans where snow and ice retreat. Somewhat larger changes are found over land masses and the Arctic while smaller increases in extreme minimum temperatures occur at the margins of the polar oceans. Thus, there is some asymmetry between the change in the extremes of minimum and maximum temperature (with a bigger increase for minima than maxima). This has to do with the change in the nature of the contact between atmosphere and the surface (e.g., minima increase sharply where ice and snow cover have retreated exposing either ocean or land, maxima increase more where the land surface has dried). Consequently there is a seasonal depend- ence related to changes in underlying surface conditions, which indroduces uncertainties in some regions in some models.
Changes in the heating and cooling degree days are another likely extreme temperature-related effect of future greenhouse warming.
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