The plant community in an area is the most sensitive indicator of climate. Areas with moderate to high temperatures and abundant rainfall throughout the year are heavily forested unless humans have cleared the land for agriculture! Areas with somewhat less rainfall are mainly grasslands, which are called prairies in North America.
Humans have converted grasslands into rich agricultural areas around the world. Tree Physiol 8 2 — Google Scholar. Den Driessche V New root growth of Douglas-fir-seedlings at low carbon dioxide concentration. Tree Physiol 8 3 — Google Scholar.
Science — CrossRef Google Scholar. Herbon Publishing, Victoria. Tree Physiol —15 Google Scholar. Luxmoore RJ CO 2 and photosynthesis. Bioscience CrossRef Google Scholar. Luxmoore RJ A source sink framework for coupling water, carbon, and nutrient dynamics of vegetation. In the past ten years there was a major slowdown in the amount of land being developed.
On average, the Southeast has twice as much developed land as the rest of the United States, although this is offset by the fact that over half of the land in the Southeast is forest. Forests are beneficial because they use copious amounts of carbon dioxide, as well as mitigating heat through transpiration. Farmers are responsible for maintaining a majority of the cropland vegetation in arable regions of the world. Vegetation or the lack of it is a key factor affecting weather patterns and micro-climates.
The following factors are affected by vegetation:. Figure C. Bradford pear orchard. Image from Bridget Lassiter. When irrigation is taken out of the equation, rain, snow, fog, dew, frost and soil water are all used and captured by vegetation. Some of this water is intercepted by the leaves themselves, and some of the water that infiltrates the soil is absorbed by plant roots.
When water is available in excess, plants can transpire large volumes of water as a by-product of photosynthesis. This in turn causes evaporative cooling in the atmosphere directly surrounding the crop. Seasonal variations have shown that higher levels of CO 2 are measured in the early-mid part of the growing season. There are also daily variations in CO 2 , with the highest levels measured during the day. The albedo of a crop is lower than the sum of all of the leaves in the canopy due to differences in crop architecture and angle of solar radiation.
But a second effect counters that: A warming world means longer and warmer growing seasons, which gives plants more time to grow and consume water, drying the land. Researchers have now shown a third effect: As CO 2 levels rise, it amps up photosynthesis. Plants in this hotter, CO 2 -rich environment grow bigger, with more leaves. That means when it rains there will be far more wet leaves creating more surface area for more evaporation to occur.
Computer modelling shows that such enhanced leaf evaporation has a large effect on runoff and soil moisture, says Mankin. Mankin's team used 16 different climate models with historical data for a number of variables including precipitation, leaf evaporation, soil evaporation, leaf area index, soil moisture, and more that accurately replicate past conditions.
Future climate variables such as surface air temperature and CO 2 levels were added to find out how they would affect the global water cycle. While plants everywhere will consume more water in a hotter, CO 2 -rich world, northern and tropical regions are projected to have enough precipitation to offset the additional plant growth, Mankin says. That will lead to water declines in rivers and streams in the mid-latitudes, including North America, Europe, and Central Asia.
Previous climate research has found an 80 percent likelihood of a year or longer "megadrought" striking the Southwest and central Great Plains by with business-as-usual CO 2 emissions.
Moderate reductions in emissions will only reduce this risk to 60 percent. And this megadrought model does not include the new findings about how changes in vegetation could worsen conditions, says Gleick.
The atmosphere is already more CO 2 rich and the climate is warmer. There is evidence from satellites showing significant increases in vegetation in the past 40 years, says Mankin. While growing seasons are also getting longer, it is difficult to say this recent greening of the Earth is entirely due to climate change because there have been so many human alterations to the landscape over the last years, he says.
For at least , years the concentration of atmospheric CO 2 levels ranged between and parts per million ppm. In the last 10, years they stayed around ppm until the Industrial Revolution sparked widespread use of coal.
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