Why Climate Change is a Clear and Present Danger: The Facts About Global Warming

According to climate scientist Andrew Emory Dessler we have a "robust understanding" of climate change that makes it hard to refute anthropogenic global warming. This article summarizes what we know about climate science.

Dessler is a climate scientist and Professor of Atmospheric Sciences at Texas A&M University. He is an expert in atmospheric chemistry, climate change and climate change policy. He has been studying the atmosphere since 1988. His peer-reviewed publications on climate change, include studies of the cloud and water vapor feedbacks and climate sensitivity.

The information presented here is a summary of his testimony regarding the most important conclusions the climate scientific community has reached in the last two centuries. He describes conclusions that scientists know to be true with a high degree of confidence.

1. The climate is warming

He points to observed increases in the temperature of the lower atmosphere and ocean spanning many decades. This includes the global average surface temperature, and ocean warming. This data is supported by a "mountain of ancillary data" including satellite measurements, ice loss and sea level rise.

2. Warming is due to Human Activities

He reviews the evidence for emissions of carbon dioxide and other greenhouse gases as the causal factor in global warming. He states that humans have increased the amount of carbon dioxide in the atmosphere from 280 parts per million in 1750 to 400 parts per million today. Methane levels have more than doubled over this period, and chlorofluorocarbons did not exist in our atmosphere before humans. He explains that the observed relationship between GHGs and warming are consistent with climate models. Far from overstating the case, he sees the IPCC's conclusions as "conservative."

3. Future warming could be large

He goes on to say that if we continue with business as usual, GHG emission will keep rising and lead to a 21st century global average warming of 4.7 - 8.6°F3. Regionally, on land and in the Arctic, the warming is apt to be larger. Such temperature increases would "herald a literal remaking of the Earth’s environment and our place within it."

4. The impacts of this are profound

The virtually certain impacts include:

increasing temperatures
more frequent extreme heat events
changes in the distribution of rainfall
rising seas
the oceans becoming more acidic

As explained by Dessler, "those impacts and their magnitude are, by themselves, sufficient to compel us to act now to reduce emissions."

Other outcomes are less well known, but could prove to be significant, this include: