A climate that's already changing
Climate is always changing, but the changes we've observed in the last several decades are best explained as a combination of natural and human-made causes.
The first IPCC report, issued in 1991, discussed changes we could expect decades in the future. Some of those are happening now, as reported in the IPCC's 2007 assessments. Our confidence in projecting future changes has also improved.
Some of the trends now under way—such as warmer nights during heat waves and heavier bursts of rain and snow—are expected to continue. Other changes will be less familiar, and there could be surprises along the way. This increased uncertainty makes planning for the future more difficult.