Climate Change in Vermont

The climate of Vermont has changed substantially in the past fifty years. Continuing change is certain, as the Earth’s climate is being driven towards a warmer mean state by the increase of greenhouse gases in the atmosphere. The primary driver is that the burning of the fossil fuels increases atmospheric CO2, which has a centennial lifetime in the atmosphere. Since CO2 is as a greenhouse gas, this reduces the longwave cooling of the Earth to space. The warming from the increase of CO2 is amplified several times1 because atmospheric water vapor, another powerful greenhouse gas, increases on monthly timescales as temperature increases. Globally some ice is melting, but the oceans are storing much of the heat that the Earth cannot radiate back to space; so the current increase in greenhouse gases will have a long-term impact lasting decades to centuries. The warming is amplified further at northern latitudes by reductions in snow and sea-ice cover2, which means less of the sun’s energy is reflected. The global atmospheric circulation is also changing in response to both the increase in greenhouse gases, and the reduction of northern sea-ice3.

We have two complementary reference frameworks when planning for the future:

1) Regional projections from climate models 2) Climate trends in Vermont and New England in recent decades

Global model projections help us look into an uncertain future and explore humanity’s options and risks. For example, we can estimate how the patterns of temperature and precipitation will change, and see how reducing greenhouse gas emissions give a smaller mean global temperature rise by the end of this century. Our models for the Earth’s climate system necessarily contain simplifications, but they are continually revised as understanding improves. In 2014, the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC-AR5, 2014)4 was completed by an international team of some 800 lead authors and 2,000 expert reviewers. This Report documented the global and regional changes in temperature and precipitation expected this century. The Third National Climate Assessment Report5 looks at climate change impacts in the US. A new Climate Change Special Report6 has been prepared by the US Global Change Research Program by scientists from the federal agencies, national laboratories and universities in preparation for the Fourth National Climate Assessment (NCA4). These quadrennial assessments were mandated by Congress in the Global Change Research Act of 1990. The current federal administration has recently disbanded the federal advisory committee to the National Climate Assessment as part of its efforts to suppress climate change science. However, Figures from this latest Report6 are included in this Vermont assessment, since they have been updated through 2016, they have been thoroughly reviewed, and are scheduled for November publication.

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