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
Other outcomes are less well known, but could prove to be significant, this include:
- increases in drought intensity and distribution
- increases in flood frequency
- stronger hurricanes
5. The Dangers of Inaction
Dessler points to newly published research (Allen and Stocker, 2014) which shows that every year we do not act to reduce GHGs commits us to about 2 percent more eventual warming. This adds to the urgency of acting soon as the longer we wait the harder it will be to limit global warming to under 2°C.
© 2014, Richard Matthews. All rights reserved.
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