What is climate change?

Increased concentrations of GHGs from anthropogenic sources have increased the absorption of infrared radiation, enhancing the natural greenhouse effect. (Image credit: Center for Sustainable Systems (CSS), University of Michigan)

Climate can be defined as the collective state of the atmosphere for a given place over a specified interval of time. There are three parts to this definition: location, because climate can be defined for a globe, a continent, a region or a city; time, because climate must be defined over a specified period; and the collective state of the atmosphere, which includes averages and extremes of variables such as temperature, precipitation, pressure and winds.

Climate change is a long-term change in the average weather patterns that have come to define Earth’s local, regional and global climates.

Climate change can result from natural events, such as volcanic eruptions, asteroid impacts or changes in our sun’s energy output.

Climate change can also be caused by human activities. The building of cities is a well-documented example of inadvertent modification of a climate by human activities. The urban heat island effect refers to the increased temperatures of urban areas compared with a city’s rural surroundings. Several factors contribute to the relative warmth of cities, such as heat from industrial activity and the thermal properties of buildings and roads.

Since the 1800s, human activities have been the main driver of observed climate change, primarily due to the burning of fossil fuels such as coal, oil and gas. Burning fossil fuels generates greenhouse gases, which are transparent to solar radiation but absorb large amounts of terrestrial infrared radiation that results in warming the atmosphere.

Over the past two centuries, the global average surface temperature has increased noticeably. Currently, Earth is about 2.11 degrees Fahrenheit warmer than the late 19th-century preindustrial average. The 10 most recent years are the warmest on record. There is no debate about the cause of this warming trend; it has resulted from human activities, principally through emissions of greenhouse gases.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, History

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What is the National Weather Service?

The logos of the National Oceanic and Atmospheric Administration and the National Weather Service (Image credit: NOAA/NWS)

The National Weather Service, or NWS, is an office of the National Oceanic and Atmospheric Administration, NOAA, which sits in the U.S. Department of Commerce. The connection to the Department of Commerce is sensible – it’s estimated that one-third of the U.S. economy is sensitive to weather and climate.

The mission of the National Weather Service is to “provide weather, water, and climate data, forecasts, warnings and impact-based decision support services for the protection of life and property and enhancement of the national economy.”

The roots of the NWS go back to Feb 9, 1870, when U.S. President Ulysses S. Grant signed a joint resolution of Congress into law establishing the Weather Bureau of the United States. It was originally placed within the U.S. Army Signal Services’ Division of Telegrams and Reports for the Benefit of Commerce. Twenty years later, on Oct. 1, 1890 at the request of President Benjamin Harrison, Congress passed a law transferring the meteorological responsibilities of the Signal Service to the newly created U.S. Weather Bureau, housed in the Department of Agriculture. The Weather Bureau became the National Weather Service in 1970 with the creation of NOAA.

The NWS and NOAA are incredible public goods. The NWS provides weather forecasts, warnings, and climate data across the U.S. and exchanges that information with weather services around the globe. The NWS and NOAA weather observations and forecasts are publicly available at no cost. Their forecasts are accurate enough that we use them daily to schedule outdoor activities, adjust travel, wear clothes appropriate for conditions and plan for impending storms. These forecasts help to save lives.

Commercial weather companies use this public data along with private and proprietary weather data and models to create industry-specific weather forecasts. Publicly available and paid weather services complement one another and keep our nation informed and prepared for coming weather events.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Uncategorized

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How unusual was our dry and warm October weather?

The National Weather Service in La Crosse says there have been precipitation deficits of 1 to 8 inches in Door County, with the greatest deficits of 4 to 8 inches south of Interstate 90. That has resulted in the dry and drought conditions for Wisconsin, Minnesota and Iowa. (Image credit: NWS-La Crosse)

Meteorologists often compare current temperature and precipitation measurements to “normal” values to interpret unusual weather. The weather data observed over the 30-year period between 1991 and 2020 are used to define “normal” or “average” weather. These normals are recalculated every 10 years. The normals are determined on annual, seasonal, monthly, daily and even hourly timescales. The maximum and minimum values also are tracked for each day of the year.

The weather that southern Wisconsin has experienced this October has been different from our normal October weather. Throughout most of October, we experienced very dry conditions. Prior to the storms that occurred on Oct. 30 and 31, the total precipitation across most of the state was less than 50% of the normal precipitation. This lack of precipitation throughout the month was alleviated during the final two days. Many areas in Dane County received over 3 inches of rain on Oct. 30 and 31.

Record warm temperatures were recorded in Madison on October 29: The high was 82 degrees Fahrenheit, tying the record high temperature for that day set in 1937 and making it only the second time we have hit 80 degrees or higher that late in the year. Also, the low temperature of 65 degrees that day set a record warm minimum temperature, breaking the old record of 63 degrees set in 1946. The National Weather Service at Green Bay also set high temperature marks: 82 degrees on Oct. 29 and 80 degrees on October 30 were new records.

The record temperatures were supported by strong winds from the south and southwest moving warm air northward. The lack of precipitation throughout most of the month has contributed to low soil moisture. These dry conditions also support warmer air temperatures.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Uncategorized

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What is a meteorological bomb?

Storm systems that form in middle or high latitudes, in regions of large temperature contrast are called extratropical cyclones. This contrasts with tropical cyclones, such as hurricanes, which form in regions or relatively uniform temperatures.

A mid-level water vapor image from GOES-West, that is, Band 9 at 6.95 micrometers.  The yellow and blue enhancements are regions where water vapor is constrained to the middle part of the troposphere; the white and green parts are where moisture is present at the top of the troposphere. (Image credit: CIMSS) 

Extratropical cyclones are surface low-pressure systems where the air at the surface flows counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. The winds around these centers of low-pressure spiral inward at the surface, forcing rising motions.  The rising air can result in clouds and precipitation. The process of extratropical cyclone development and intensification is referred to as cyclogenesis. In North America there are favorable regions for cyclogenesis, including the eastern slopes of mountain ranges, the Atlantic Ocean off the Carolina Coast, and the Gulf of Mexico. The jet stream also influences cyclogenesis.

The polar jet stream is a zone of faster moving air in the upper troposphere. Its meandering pattern has regions of convergence and divergence. The position of the jet stream influences cyclogenesis. To maintain a low pressure at the surface, the rising air associated with the surface convergence, must transported away at the top of the developing storm. The upper air divergence associated with a jet stream maintains the low pressure at the surface, by removing air from the column, reducing its weight and causing the pressure to fall at the surface.

During cyclogenesis the surface pressure in the storm is decreasing. How fast the surface pressure decreases is an indication of how the storm is developing.

A ‘meteorological bomb’ is an unofficial term for very rapid, or explosive, cyclogenesis. It is defined as when the central pressure of a developing extratropical cyclone falls 24 millibars in 24 hours.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Phenomena, Severe Weather

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Science-based policy is shrinking ozone hole

The Southern Hemispheric ozone hole usually begins to develop in mid- to late August, as the hemisphere emerges from its winter, and peaks in mid-October.

The Antarctic ozone hole — the total area where ozone amounts are below 220 Dobson units — on September 21, 2023, the day of its largest extent for the year. The annual maximum extent of the ozone hole in 2023 (light purple bar, measured in millions of square kilometers) compared to all years in the satellite record (dark bars). NOAA Climate.gov image based on NOAA (map) and NASA (graph) satellite data. (Image credit: NOAA)

This year it first appeared closer to the end of August and by mid-September was 18.48 million square kilometers in size, smaller than in recent years, including both 2022 and 2023. Though this year’s slow start does not necessarily reflect a recovery of the ozone layer, it does support the notion that expert guidance has made a positive contribution to this vexing problem.

Just a few years after the ozone hole was detected via satellite, the industrialized nations of the world, meeting in Montreal in 1987, adopted what is known as the Montreal Protocol. That international agreement, based upon the consensus scientific understanding of the problem, placed prudent restrictions on the use of chlorofluorocarbons, or CFCs.

The result of this scientifically informed policy-making has been a gradual but systematic healing of the ozone hole. Despite the success of the Montreal Protocol, current estimates are it will require another four decades, if the protocol is followed, before recovery toward pre-ozone hole conditions.

This success should serve as a leading example of the power of scientific analysis and understanding to shape important environmental policy.

The world is facing a slower-burning crisis as a result of human-induced changes to the atmosphere that are, in turn, compelling a change to a warmer climate. There is no lack of scientific consensus of the roots of this problem nor any shortage of science-based prescriptions for seeking its remedy.

The time has long passed for our society to seriously debate, and then begin to take, the bold actions necessary to meet this crisis. Our scientific and industrial infrastructure is more than sufficient to meet this pressing challenge — we have successfully done so before!

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: History, Phenomena

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