Q:  Why was this project undertaken?

A:  The historical analysis and future projections of Wisconsin’s climate were done for the Wisconsin Initiative on Climate Change Impacts (WICCI), a collaborative project of the University of Wisconsin and the Wisconsin Department of Natural Resources (DNR).  WICCI is coordinated by the Nelson Institute for Environmental Studies at the University of Wisconsin-Madison; the climate analyses were done in the Nelson Institute’s Center for Climatic Research and Center for Sustainability and the Global Environment.

Working groups of scientists in WICCI are assessing the potential impacts of climate change on natural and human systems across the state, including wildlife habitat, water resources, forestry and agriculture, tourism, human health, urban conditions, stormwater management and others.  These working groups need future climate projections to evaluate specific potential consequences on those resources and systems; the working groups will then develop recommendations on how to adapt.  The primary purpose of these analyses is to enable the WICCI working groups to move ahead on impact assessments based on a clear and consistent set of climate data specific to Wisconsin.

Wisconsin’s Focus on Energy was the primary source of funding for the climate research, with additional support coming from UW-Madison and the DNR. Focus on Energy is a non-profit, public-private organization that helps Wisconsin residents and businesses manage rising energy costs, promote in-state economic development, protect the environment and control the state's growing demand for electricity and natural gas.  

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Q:  Is Wisconsin’s climate changing?

A:  Yes.  Information gathered from weather stations across Wisconsin over the past few decades indicate that the state has been warming consistent with the global pattern.  On an annual average, Wisconsin warmed about 1.1 degrees Fahrenheit between 1950 and 2006; the northwestern part of the state has warmed a bit more than the rest.  Winter temperatures have risen most significantly.  Statewide, winter temperatures have increased 2.5°F, while increases of 3.5-4.5°F have occurred in northwestern Wisconsin.  Summer and autumn temperatures in Wisconsin have changed the least.

Precipitation patterns have also changed.  Wisconsin as a whole has become wetter, with an increase in annual precipitation of 3.1 inches from 1950 to 2006.  Most of the increase has been concentrated in southern and western Wisconsin, with increases ranging from 3 to 7 inches per year by the end of the 57-year period.  Northern Wisconsin has become drier, annually averaging 1-2 inches less precipitation over that period.

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Q:  Are these changes likely to continue into the future?

A:  Yes, and they are likely to intensify.  Climate models, run on some of the most powerful supercomputers in the world, show that significant changes are highly probable across Wisconsin.  The state is projected to warm by 4 to 9°F by the middle of this century, based on the A1B emission scenario (explained below).  Northern Wisconsin is projected to warm the most, while the least warming is expected along Lake Michigan. The average mean projected warming rate is about four times greater than what has been observed since 1950.

The warming is projected to be largest in winter, with projected increases of 5 to 11°F by the mid-21st century across Wisconsin, with the greatest warming in northwestern Wisconsin.

The majority of climate models simulate an increase in annual precipitation across Wisconsin, with the greatest, most robust increases across northern Wisconsin.  Across southwestern Wisconsin, the projected increase is weaker and less certain among the models.  But the models robustly agree that annual precipitation will increase, especially in winter and spring, and that Wisconsin will experience more extreme precipitation events.

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Q:  How do you know that carbon dioxide and other greenhouse gases are to blame, and not other factors, such as volcanoes, solar output or natural cycles?

A:  Climate models help answer this question.  Factors such as volcanic eruptions, solar radiation and changes in Earth’s orbit are fed into the supercomputer models.  When they are run without the observed increases in carbon dioxide and other greenhouse gases in the atmosphere, the models do not produce a warming trend.  When the greenhouse gases are added, the models reproduce the observed warming.  Thus, these results show that rising levels of greenhouse gases, produced by human activities, are warming the planet.

Greenhouse gases, by their nature, allow shortwave (mostly ultraviolet) radiation from the sun to pass through the atmosphere to the Earth's surface.  This radiation is re-emitted by the Earth as long-wave (infrared) radiation, which is trapped and absorbed by greenhouse gases, making the Earth's surface warmer. So it's logical to expect that a planet with increasing levels of greenhouse gases would become warmer.  An example is Venus, which is dramatically hotter than can be accounted for by solar energy alone.  The excess heat is due to large quantities of carbon dioxide in its atmosphere.

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Q:  How do climate models work?

A:  A climate model is a network of computer programs that together simulate the Earth system, representing physical laws and chemical interactions. A global climate model (GCM) uses hundreds of mathematical equations to describe processes such as wind, ocean currents, ice, hydrology and plant growth and how they relate to each other.  The accuracy of the models is tested by comparing simulations of past climate with actual observations.  The Wisconsin climate team used daily output from 14 different GCMs, a technique known as “ensembling.”  This brings balance to, and allows greater confidence in, the modeling results.

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Q:  What is downscaling?

A:  Global climate models are good at characterizing the large-scale atmospheric circulation of the whole planet, but their output is too coarse and too low in resolution to give a clear picture of specific regions or states.  They also do not incorporate landscape features, water bodies or other characteristics that may influence regional or local climate.  A number of methods have been developed to derive detailed regional and local climate data to evaluate the potential impacts of climate change. The Wisconsin climate scientists use a statistical method, which they believe is most accurate and flexible and represents the state of the art in climate model downscaling techniques.

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Q:  What assumptions about carbon emissions were used in the Wisconsin calculations?

A:  The future projections for Wisconsin were based on something called the A1B emissions scenario, developed by the United Nations Intergovernmental Panel on Climate Change (IPCC).  The IPCC constructed a range of scenarios, each with different levels of economic growth and greenhouse gas emissions. The A1B had been considered a moderate scenario; however, actual emissions are exceeding those embedded in the A1B, making it an increasingly conservative assumption.  The Wisconsin scientists ran projections on three scenarios – A2, A1B, and B1 – but the A1B is believed to be closest to reality at this time.

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Q:  How much uncertainty is there in these projections?

A:  We cannot know the future, and the Wisconsin scientists do not claim to.  However, they can develop a range of probable outcomes, called “probability distribution functions.”  That’s what they’ve done here.  Each projection represents a range of possibilities, rooted in past observations and current trends, carried into the future according to the laws of physics.  Scientists have a great deal of confidence when virtually all the models agree on an outcome (for example, rising winter temperatures).  They do not have high confidence when the models give a variety of outcomes, which is the case here for summer precipitation patterns.

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Q:  Has this work been peer-reviewed?

A:  The modeling methods used in this study have all been peer-reviewed and are accepted as best practices in climate science.  All of the findings, including the warming, increased precipitation and increased precipitation extremes for Wisconsin, are consistent with the IPCC 4th Assessment Report, which earned the Nobel Prize for its thoroughness.  And all the climate models analyzed have been used in peer-reviewed papers by other organizations. The historical analysis done here has been submitted for publication and is in peer review; the modeled future projections will be submitted for publication in the next few months.  The WICCI Science Council, a group of 22 eminent scientists from around the state, has “vetted” and approved these results and feels that they are important to regional, state and local decision making efforts and should be publicly shared at this time.

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Q:  What should Wisconsin do about these findings? 

A:  The results reported here are the product of scientific inquiry and are not meant to serve as policy prescriptions.  They will be used by WICCI working groups to look at how climate change might impact a variety of natural resources, ecosystems, infrastructure and economic activities.  The results can also be used by government agencies, communities, businesses, organizations and individuals to help them think about changes that Wisconsin might experience in coming decades, what those changes could mean, and, if necessary, how to develop adaptation strategies to cope with them.

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Q:  Is WICCI part of the Governor’s Task Force on Global Warming?

A:  Yes, WICCI will be collecting and assessing scientific data on climate change in Wisconsin and its impacts. WICCI will be working with the Task Force to share and tailor our findings, so that the information is incorporated into the recommendations of the Task Force.

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