The Increasing Pace of Climate Change

Abstract

Combustion of coal, oil, and natural gas and, to a lesser extent,
deforestation, land-cover change, and emissions of halocarbons and other
greenhouse gases, are rapidly increasing the atmospheric concentrations
of climate-warming gases. The resulting warming of about 0.1 to 0.2°C
per decade that has taken place over the last several decades is very
likely the primary cause of the loss of snow cover and Arctic sea ice, the
more frequent occurrence of very heavy precipitation, rising sea level,
and shifts in the natural ranges of plants and animals. Global average
temperature is already ~0.8ºC above its preindustrial level. As expected,
warming has been greater in mid and high latitudes compared to low
latitudes, over land compared to oceans, and at night compared to day.
The present atmospheric levels of long-lived greenhouse gases are
pushing toward further warming of ~1.0-1.5ºC. This further warming is
being held back by the time it takes for the oceans to warm and by the
cooling influence of short-lived sulfate aerosols. As a result, at least as
much further warming as has occurred to date would be expected even
if global greenhouse gas emissions could be immediately cut to zero. At
their present rate, ongoing emissions and the past commitment to warm-
ing are projected to lead to further warming at a rate of ~0.2-0.3ºC per
decade over the next several decades, especially if emission controls are
not put in place. Such warming and the associated changes are likely to
cause severe impacts to key societal and environmental support systems.
Present estimates are that reducing emissions sharply by 2050 and to
near zero by 2100 will be required to limit the increase in global average
surface temperature to no more than 2 to 2.5°C above its 1750 value of
about 15ºC, and that this will be necessary to avoid the most catastrophic,
but certainly not all, consequences of climate change.