Scientists have already shown significant alteration of the American landscape because of increased CO₂ emission from burning fossil fuel, which causes global warming. But, pressured by various lobbies (mainly oil and auto industries), the US government has been dragging its feet over acknowledging that global warming is indeed a serious threat.

Until now, that is. Bowing to a district court judge’s ruling that the government must produce the latest scientific assessment of global warming by May 31, the Climate Change Science Program, which was commissioned by USDA and integrates the federal research efforts of 13 agencies on climate and global change, released its findings on May 27.

The study, which was carried out by 38 scientists from inside the government and outside (universities, national laboratories and non-governmental organizations), includes no new research, but synthesizes a thousand scientific papers to highlight how the human-generated CO₂ emission has already caused major changes in our environment.

From the press release, the main points of the study are:

1. Increasing temperatures will increase the risk of crop failures, particularly if rainfall decreases and/or becomes more unpredictable.
2. Higher temperatures will reduce productivity of livestock and dairy animals, and greater mortality will offset the reduced mortality in warmer winters.
3. Climate change has already increased the size and frequency of forest fires, insect outbreaks and tree mortality, in the forests of interior West, Southwest and Alaska. These effects will continue.
4. The West and Southwest have also experienced increased draught conditions.
5. Weeds grow more rapidly under high atmospheric CO₂, and they are expected to migrate northward and be resistant to herbicides.
6. Invasion by exotic grass species into arid lands will increase, causing higher fire frequency, which in turn will affect rivers and riparian systems in these areas.
7. Horticultural crops (tomato, onion, fruit) are more sensitive to climate change than grains and oilseed crops.
8. The length of the growing season has increased by 10 to 14 days over the last 19 years across the temperate latitudes, and species distributional ranges have shifted as a result.
9. Arctic snow and ice covers have dramatically declined because of warming, and the resulting habitat loss is threatening the wildlife, such as the polar bear, that depend on ice.