The Earth has grown warmer by about one degree in the last century and scientists believe the process is accelerating. At the 1992 Earth Summit in Rio de Janeiro the United States vowed to reduce its share of greenhouse-gas emissions to 1990 levels by the year 2000, but it now seems apparent that this goal will not be met. There are myriad marginal costs associated with the combustion of fossil fuels. Listed as endpoints are mortality, heart attacks, strokes, hospital admissions, respiratory illness, work loss days, restricted activity days, asthma attacks, IQ changes, hypertension, decreased worker productivity, visibility, household soiling, and agriculture. Most of the net benefits resulted from reductions of lead and particulate matter.
Carbon dioxide is the primary greenhouse gas.
Current rates of deforestation and combustion of carbon-based fuels like petroleum and coal are adding carbon dioxide into the atmosphere faster that the oceans can absorb it, trapping heat in Earth's atmosphere. According to IPCC, carbon dioxide lingers in the atmosphere for many decades, meaning that actions taken to diminish the risks of climate change will take effect several years after their introduction. Some petroleum and coal industry representatives have argued that the threat of climate change from heat -trapping industrial emissions is overblown, and countries should wait for more scientific proof of global warming before they implement policies to slash emissions. Some energy and utilities industries have shifted their strategy from attacking the scientists to warning of prohibitively expensive costs of enacting policy changes to slow climate change. But using such models on a decades-long, dynamic, global issue such as climate change is a distortion of the intended use of modeling, at best.