Human‐Induced Climate Change Requires Urgent Action
Humanity is the major influence on the global climate change observed over the past 50 years.
Rapid societal responses can significantly lessen negative outcomes.
Human activities are changing Earth’s climate. At the global level, atmospheric
concentrations of carbon dioxide and other heat‐trapping greenhouse gases have increased
sharply since the Industrial Revolution. Fossil fuel burning dominates this increase.
Human‐caused increases in greenhouse gases are responsible for most of the observed
global average surface warming of roughly 0.8°C (1.5°F) over the past 140 years. Because
natural processes cannot quickly remove some of these gases (notably carbon dioxide)
from the atmosphere, our past, present, and future emissions will influence the climate
system for millennia.
Extensive, independent observations confirm the reality of global warming. These
observations show large‐scale increases in air and sea temperatures, sea level, and
atmospheric water vapor; they document decreases in the extent of mountain glaciers,
snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with longunderstood
physics and predictions of how the climate system is expected to respond to
human‐caused increases in greenhouse gases. The changes are inconsistent with
explanations of climate change that rely on known natural influences.
Climate models predict that global temperatures will continue to rise, with the amount of
warming primarily determined by the level of emissions. Higher emissions of greenhouse
gases will lead to larger warming, and greater risks to society and ecosystems. Some
additional warming is unavoidable due to past emissions.
Climate change is not expected to be uniform over space or time. Deforestation,
urbanization, and particulate pollution can have complex geographical, seasonal, and
longer‐term effects on temperature, precipitation, and cloud properties. In addition,
human‐induced climate change may alter atmospheric circulation, dislocating historical
patterns of natural variability and storminess.
http://sciencepolicy.agu.org/files/2013/07/AGU-Climate-Change-Position-Statement_August-2013.pdf