Is human activity to blame for climate change?

A recent debate between candidates for Congress in the Wisconsin’s 1st District — U.S. Rep. Paul Ryan, R-Janesville, and Democratic challenger Rob Zerban — included questions about the role of human beings in producing discernible changes in the climate over the last 150 years.

Unfortunately, this question, which is a matter of evidence, analysis and conclusion as all scientific questions are, has become a source of partisan political divide.

The Intergovernmental Panel on Climate Change (IPCC), a scientific body created by the United Nations to inform the UN regarding “scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change,” has issued five reports on this question since 1990.

These reports are a synthesis of many hundreds of peer-reviewed scientific studies on the issue.

With each successive report — they have been issued in 1995, 2001, 2007 and 2014 — the IPCC has increased the certainty of its conclusions.

The language in these reports has changed from “the balance of evidence suggests a discernible human influence on global climate” (1995) to “most of the observed warming is likely (a greater than 66 percent chance) due to human activities” (2001) to warming “over the last 50 years is very likely (a greater than 90 percent chance) due to human activities” to “It is extremely likely (a 95-100 percent chance) that human influence was the dominant cause of global warming between 1951-2010.”

This makes two things quite clear.

First, that scientists are a skeptical bunch and will move toward increased certainty only as evidence accumulates in favor of that conclusion.

Second, that human-induced global warming is a reality with which we must reckon.

During the debate, when asked if humans have a role in global warming, Ryan answered, “I don’t know the answer to that question. I don’t think science does either.”

He may well be correct in his first response, but he is certainly wrong in his second.

Category: Climate

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What happened during last week’s lunar eclipse?

What happened during last week’s lunar eclipse?

Our recent lunar eclipse, visible in Madison at 5:25 a.m. Wednesday, resulted from the Earth being directly between the sun and the moon, thereby casting a shadow on the moon.

The degree of directness of the shadow determines the degree of completeness of the eclipse.

We were lucky enough to see a total lunar eclipse in this part of the country. In addition, we were fortunate that the sky was perfectly clear as it has been quite often during our recent beautiful autumn weather.

The timing of the eclipse, coupled with the perfectly clear skies, also delivered a rare selenelion – an event characterized by the simultaneous appearance of the sun and the lunar eclipse.

This was visible in Madison at 7:03 a.m. and was captured by the rooftop cameras on the Atmospheric, Oceanic and Space Sciences building on UW-Madison’s campus.

One might wonder how both the sun and the eclipse can be visible at the same time given that the eclipse is a result of the moon being directly in the shadow of the Earth. The answer is that the Earth’s atmosphere refracts, or bends, light that is traveling through outer space because the atmosphere is more dense than the vacuum of deep space.

This bending of light is the same type of phenomena that renders the illusion of a spoon being discontinuous at the fluid-air boundary in a clear glass of water.

The refraction in the selenelion case “lifted” the images of the sun and the eclipsed moon slightly above the horizons.

Had the sunrise been at a slightly different time, or had there been low clouds on either horizon at sunrise on Wednesday, we would not have been lucky enough to catch the rare selenelion in the act.


Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

Category: Meteorology, Phenomena

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What is the status of the ozone hole?

Ozone occurs about 18 miles above the surface. Ozone is both caused by and provides protection from damaging ultraviolet energy emitted by the sun. The development of an atmospheric “ozone layer” allowed life to move out of the oceans and onto land.

The ozone hole occurs high over the continent of Antarctica. It is not actually a hole, but rather the appearance of very low values of ozone in the stratosphere. Typically, the Antarctic ozone hole has its largest area in early September and lowest values in late September to early October.

The Antarctic ozone hole varies in size each year, from nearly zero in 1980 to an area larger than North America in 2000. The amount of ozone in the atmosphere is now routinely measured from instruments flying on satellites.

The size of this year’s ozone hole reached a maximum size in September of about 7 million square miles. It is about the same size as the ozone hole in 2011 and 2012.

The ozone hole forms through the destruction of ozone over Antarctica. The winter atmosphere above that continent is very cold. The cold temperatures result in a temperature gradient between the South Pole and the Southern Hemisphere middle latitudes, which results in strong westerly stratospheric winds that encircle the South Pole region.

These strong winds prevent warm air from the equator from reaching these polar latitudes. These extremely cold temperatures inside the strong winds help to form unique types of clouds called polar stratospheric clouds, or PSCs.

PSCs begin to form during June, which is winter time at the South Pole. Chemicals on the surface of the particles composing PSCs result in chemical reactions that remove the chlorine from the atmospheric compounds. When the sun returns to the Antarctic stratosphere in the spring (our fall), sunlight splits the chlorine molecules into highly reactive chlorine atoms which rapidly deplete ozone. The depletion is so rapid that it has been termed a “hole in the ozone layer.”

Thanks to the Montreal Protocol’s phased global ban on chlorofluorocarbon (CFC) use and the natural decay of these chlorine compounds, the stratosphere will be CFC-free near the end of the 21st century. In their absence, the ozone layer will repair itself naturally.

The good news is that the size of this ozone hole is showing signs of shrinking. This recovery is a prime example of the power of employing science research in the shaping of public policy.

We would be wise to learn from this example to inform our collective approach to climate change.

Category: Climate, Meteorology

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What is the meteorological origin of these beautiful fall days?

The beautiful, crystal clear early fall days that we have recently enjoyed are characteristic of September in southern Wisconsin.

Such days are often quite cool to start, with morning temperatures in the 40s, but often warm by late afternoon when temperatures can soar to the mid- to high 70s.

Such conditions are associated with regions of high pressure either migrating past us or developing over us.

These high pressure regions are characterized by gentle, persistent sinking of the air from the middle troposphere to the surface – most times are rates of only about 150 feet per hour.

The sinking forces the air to warm by compression which reduces the relative humidity, accounting for the deep blue skies.

The clear skies, extending into the overnight hours in such episodes, allow for substantial cooling of the surface by radiation so that the temperature can be quite low by the time the sunrise occurs again, more than 12 hours later.

(Don’t forget that by late September, after the equinox, the night is longer than the day).

The development of regions of high pressure is now well understood to be associated with the passage of upper-tropospheric “ridges” in the flow.

These ridges are regions where the upper-level flow of air is constrained to turn clockwise over horizontal distances of hundreds of miles.

On the eastern edge of such clockwise turning flow regions, the laws of physics compel the air to gently sink and a high-pressure region is either newly created or sustained in that location.

The unsettled weather that accompanies a surface low-pressure region compels us to refer to it as a “storm.”

Though it is not common to refer to high-pressure regions as “storms,” they are, just like their low pressure counterparts, spawned by the passage of upper-tropospheric waves.

In fact, the longest-lived storm in the solar system (as far as we know) is a region of high pressure – Jupiter’s Great Red Spot.

Category: Meteorology, Seasons

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Do September temperatures foretell the nature of the winter?

After the recent abnormally cold period, which has left us 3.2 degrees colder than normal thus far in September, a lot of people have been wondering if September temperatures can be a harbinger of what is to come in the winter.

Everyone recalls last winter as a persistently cold season during which we experienced a four-month period (December 1 – March 31) with an average temperature that was 7.44 degrees below normal. Interestingly, last September was 2.7 degrees above normal and last October was 1.0 degrees above normal.

Records from the preceding four winters (2009-10 through 2012-13) provide an interesting, though inconclusive, answer to this question. Of those four prior winters (December through February only), two were colder than normal — 2009-10 by 0.26 degrees and 2010-11 by 1.50 degrees. In 2010-11, September and October averaged 1.67 degrees warmer than normal, while in 2009-10 those same months were 1.14 degrees colder than normal.

The winters of 2011-12 and 2012-13 were 7.01 and 1.32 degrees warmer than normal. Their corresponding Septembers/Octobers were 0.74 degrees warmer and 0.35 degrees colder than normal.

Thus, based upon a very small but recent sample, one might tentatively conclude that abnormal cold or warmth in September and October has little to do with the nature of the coming winter. The most recent three-month outlook issued by the Climate Prediction Center is equally inconclusive for the Midwest, suggesting equal chances for colder- or warmer-than-normal conditions for our months of September, October and November.

Category: Climate, Meteorology, Seasons

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