NIPCC Report Summary for Policymakers
Few scientists deny that human activities can have an effect on local climate or that the sum of such local
effects could hypothetically rise to the level of an observable global signal. The key questions to be
answered, however, are whether the human global signal is large enough to be measured and if it is, does it
represent, or is it likely to become, a dangerous change outside the range of natural variability?
NIPCC’s conclusion, drawn from its extensive review of the scientific evidence, is that any human global climate signal is so small as to be embedded within the background variability of the natural climate system and is not dangerous. At the same time, global temperature change is occurring, as it always naturally does. A phase of temperature stasis or cooling has succeeded the mild twentieth century warming. It is certain that similar natural climate changes will continue to occur.