The Earth was a much colder and drier place then. Deserts were more extensive, summers were short, and winters brutal. At the peak of glaciation, oceans were 300 feet lower than they are today, allowing animals and men to walk from Siberia to Alaska across the Aleutian Land Bridge, causing changes to the ecosystem of North America. It wasn't until about 15,000 years ago that global warming caused the great glaciers to retreat, allowing establishment of our accustomed environment. The Role of the Greenhouse Effect F rom an historical perspective, global warming has saved us, at least temporarily, from an Icehouse Climate, although humans can hardly take the credit.
Science is clear on what controls cycles of climate change.
Human's did not cause the greenhouse effect, but critics maintain human additions to atmospheric greenhouse gases may cause global temperatures to rise too much. If we are in fact in a global warming crisis, even the most aggressive and costly proposals for limiting industrial carbon dioxide emissions would have an undetectable effect on global climate. However, significant efforts to limit the emission of greenhouse gases in the United States are currently underway. While scientists are currently searching for proof that emissions from the burning of fossil fuels are warming the planet, there exists no solid proof at this time. Right now I do not have confidence that changes in sea ice and clouds are done correctly in climate models.