If you are like me, when something crosses your mind that you wonder about, you go research it to the best of your ability. Everyone has an opinion, but what about the data to support it? Let’s look at this business of weather and climate. Is there a difference between the two? There are some terms we need to define to understand what we are talking about.
Think of weather as a brief snapshot of activity and climate as the overall picture. More technically, weather is the state of atmosphere-ocean-land conditions (hot/cold, wet/dry, calm/stormy, sunny/cloudy) that exist over relatively short periods like hours or days. Weather includes the passing of a thunderstorm, a hurricane, blizzard or a cold snap, hot or cold days, severe storm events or clear days. Weather variability and extreme events may respond unpredictably in response to climate change.
We generally look at Climate as Tropical, Dry, Temperate, Cold and Polar. Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It is the long-term weather of that area (at least 30 years). This includes the region's general pattern of weather conditions, seasons and weather extremes like hurricanes, droughts, or rainy periods. Two of the most important factors determining an area's climate are air temperature and precipitation.
Let’s look first at what causes our weather patterns, then at the elements affecting climate. If we look at weather news (I suppose all of us do) then we have heard the terms like El Niño, La Niña, The Gulf Stream, The Jet Stream, highs and lows, warm front, cold fronts, etc.
Our weather in the United States moves from west to east. This is principally due to the earth’s rotation. It starts somewhere in the Pacific Ocean and crosses the country. It is said that we are currently under the influence of El Niño
El Niño is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which is characterized by unusually cold ocean temperatures in the Equatorial Pacific. El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. One consequence is increased rainfall across the southern tier of the US. We have certainly seen that of late.
The impacts of El Niño and La Niña at these latitudes are most clearly seen in wintertime. In the continental US, during El Niño years, temperatures in the winter are warmer than normal in the North Central States, and cooler than normal in the Southeast and the Southwest. During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest
El Niño is Spanish for “the little boy” or “Christ child.” This warm deep-water ocean current was discovered by fisherman long ago off the north-west coast of South America. It is called the “Christ child” because it begins around December 25th. La Niña means “the little girl” in Spanish. But it is also referred to as El Viejo, “the old one.”
If weather patterns change and persist over time, the climate is subject to change. Let’s look at the things that influence our climate.
Latitude
The latitude of an area—that is, its distance from the Equator—determines the amount of heat it receives from the sun. Close to the Equator, the sun's rays fall nearly vertically on the earth's surface most of the year. North or south of the tropics, the rays always reach the earth at a slant. Where the rays fall at a slant, they provide less warmth because they are spread out over a larger area.
Altitude
As the altitude, or height above sea level, increases, the temperature decreases at a rate of about 1 degree F. for each 300 feet. The thinner air at higher altitudes does not hold the heat radiated from the earth; this heat escapes into space. Even near the Equator, the climate at high altitudes may be extremely cold, as on Africa's snowcapped Mount Kenya.
Winds
Prevailing winds carry the heat and moisture content of the areas where they originate to other areas. The winters of Sitka, in southern Alaska, because of southwesterly winds off the warm Pacific Ocean, are as warm as those of Philadelphia, 1,000 miles closer to the Equator.
Large Bodies of Water
A body of water heats and cools much less rapidly than land does. A large body of water, therefore, provides a cooling effect in the summer and a warming effect in the winter, particularly where the prevailing winds blow onshore. In contrast, areas of land far from any large body of water tend to have larger temperature variations with the seasons. For example, the difference between the average temperatures of the warmest and coldest months in San Francisco, on the Pacific Ocean, is only 11 degrees F. In Kansas City, Missouri the difference is 51 degrees F.
Now that we know a little about our weather and climate, what about the question at hand concerning global warming. Temperatures on land and sea began to be taken around the world about 1854, but not until 1880 were there enough measuring posts to be effective for gauging climate. We then developed some 8,000 locations where daily temperatures are taken. We have kept track of temperatures for the last 130 years. So what have we learned?
According to the National Oceanic and Atmospheric Association (NOAA), our global temperature has been on the rise for the last thirty years (Note the chart from the National Climatic Data Center) which shows the annual global temperature anomalies. The term “temperature anomaly” means a departure from a reference value or long-term average. A positive anomaly indicates that the observed temperature was warmer than the reference value, while a negative anomaly indicates that the observed temperature was cooler than the reference value.
According to the scientific data, the earth seems to be getting warmer. OK, so what? Does this have any effect on us? Besides the fact they we may sweat a little more, it can have far reaching effects. How is that? It seems pretty cold right now in parts of the country that should be warmer. How does that reconcile with a warming climate?
Go back to our photo analogy. Zoom in on the top of a photograph and you see a snow covered mountain. Zoom in on the bottom and you see a warm sandy beach. Zoom out and you see the whole picture containing both views. The outward zoom is the climate. The inward zoom is the weather. Gradual changes in the climate can cause extreme changes in the weather, both hot and cold. Never before in the history of records has all 50 states had snow on the ground at the same time, as happened on February 12th of this year.
Ocean currents also play an important part in determining climate. They carry heat from the tropics toward the poles. For example, the warm waters of the Gulf Stream help keep the British Isles and northwestern Europe much warmer during the winter than they would otherwise be, giving them mild seasons. The same is true of the east coast of the US. (See map of Gulf Stream.) Is this warm Gulf Stream subject to change? If so, what can happen?
It has been reliably shown that the polar ice caps are melting at an alarming rate. Arctic sea ice extent, which is measured from passive microwave instruments onboard NOAA satellites, usually expands during the cold season to a March maximum, then contracts during the warm season to a September minimum. According to NOAA's National Snow and Ice Data Center, the September Northern Hemisphere average sea ice extent was 23.8 percent below the 1979-2000 average—the third lowest since satellite records began in 1979, behind 2007 and 2008.
The past five years have had the five smallest minimum sea ice extent on record. The September 2009 Arctic sea ice extent was 1.1 million square kilometers greater than 2007's record low and 690,000 square kilometers greater than September 2008, the second-lowest extent. This was the 13th consecutive September with sea ice extent below average. September 1996 was the last year with above-average sea ice extent.
Quoting an article by Thom Hartman (See reference below) here's how it works.
In quick summary, if enough cold, fresh water coming from the melting polar ice caps and the melting glaciers of Greenland flows into the northern Atlantic, it will shut down the Gulf Stream, which keeps Europe and northeastern North America warm. The worst case scenario would be a full blown return of the last ice age in a period as short as 2 to 3 years from its onset and the mid-case scenario would be a period like the "little ice age" of a few centuries ago that disrupted worldwide weather patterns leading to extremely harsh winters, droughts, worldwide desertification, crop failures, and wars around the world.
If you look at a globe, you'll see that the latitude of much of Europe and Scandinavia is the same as that of Alaska and permafrost locked parts of northern Canada and central Siberia. Yet Europe has a climate more similar to that of the United States than northern Canada or Siberia. Why?
It turns out that our warmth is the result of ocean currents that bring warm surface water up from the equator into northern regions that would otherwise be so cold that even in summer they'd be covered with ice. The current of greatest concern is often referred to as "The Great Conveyor Belt," which includes what we call the Gulf Stream.
The Great Conveyor Belt, while shaped by the Coriolis effect of the Earth's rotation, is mostly driven by the greater force created by differences in water temperatures and salinity. The North Atlantic Ocean is saltier and colder than the Pacific, the result of it being so much smaller and locked into place by the Northern and Southern American Hemispheres on the west and Europe and Africa on the east. As a result, the warm water of the Great Conveyor Belt evaporates out of the North Atlantic leaving behind saltier waters, and the cold continental winds off the northern parts of North America cool the waters. Salty, cool waters settle to the bottom of the sea, most at a point a few hundred kilometers south of the southern tip of Greenland, producing a whirlpool of falling water that's 5 to 10 miles across. While the whirlpool rarely breaks the surface, during certain times of year it does produce an indentation and current in the ocean that can tilt ships and be seen from space (and may be what we see on the maps of ancient mariners).
This falling column of cold, salt laden water pours itself to the bottom of the Atlantic, where it forms an undersea river forty times larger than all the rivers on land combined, flowing south down to and around the southern tip of Africa, where it finally reaches the Pacific. Amazingly, the water is so deep and so dense (because of its cold and salinity) that it often doesn't surface in the Pacific for as much as a thousand years after it first sank in the North Atlantic off the coast of Greenland.
The out-flowing undersea river of cold, salty water makes the level of the Atlantic slightly lower than that of the Pacific, drawing in a strong surface current of warm, fresher water from the Pacific to replace the outflow of the undersea river. This warmer, fresher water slides up through the South Atlantic, loops around North America where it's known as the Gulf Stream, and ends up off the coast of Europe. By the time it arrives near Greenland, it's cooled off and evaporated enough water to become cold and salty and sink to the ocean floor, providing a continuous feed for that deep sea river flowing to the Pacific. These two flows warm, fresher water in from the Pacific, which then grows salty and cools and sinks to form an exiting deep sea river are known as the Great Conveyor Belt.
So, what do we get from all this? We learn that the weather is stranger than it has been in a very long time. The polar ice is melting. Such events could affect many areas of our planet and thus our life. But the question remains. What is really causing all this change and what are we going to do about it? Is it caused by greenhouse gases or the diminishing forests of the world, or as has been suggested by some, methane gas emission caused by large quantities of cow poop?
I don’t have the answer, but I do lament all the political haranguing attached to the question. The world seems to agree there is a problem. Now, let’s see what we can do to correct it.
References
Mears, CA, FJ Wentz, 2009, Construction of the RSS V3.2 lower tropospheric dataset from the MSU and AMSU microwave sounders. Journal of Atmospheric and Oceanic Technology, 26, 1493-1509.
Mears, CA, FJ Wentz, 2009, Construction of the Remote Sensing Systems V3.2 atmopsheric temperature records from the MSU and AMSU microwave sounders. Journal of Atmospheric and Oceanic Technology, 26, 1040-1056.
Smith, T. M., and R. W. Reynolds (2004), Improved extended reconstruction of SST (1854-1997), J. Climate, 17, 2466-2477.
Smith, T. M., et al. (2008), Improvements to NOAA's Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006), J. Climate, 21, 2283-2293.
Hartmann, Thom (2004), How Global Warming May Cause the Next Ice Age, Common Dreams.org.
.The complete land-sea surface climatology from the Climate Research Unit is described in:
Jones, P. D., M. New, D. E. Parker, S. Martin, and I. G. Rigor (1999), Surface Air Temperature and its Changes Over the Past 150 Years, Rev. Geophys., 37(2), 173—199.
Global land areas, excluding Antarctica, described in:
New, M. G., M. Hulme and P. D. Jones, in press: Representing 20th century space-time climate variability. I: Development of a 1961-1990 mean monthly terrestrial climatology. J. Climate.
Global oceans, 60S-60N, described in:
Parker, D. E., M. Jackson and E. B. Horton, 1995: The GISST2.2 sea surface temperature and sea-ice climatology. Climate Research Technical Note, CRTN 63, Hadley Centre for Climate Prediction and Research, Bracknel, UK.
Arctic sea areas, described in:
Rigor, I. G., R. L. Colony and S. Martin, submitted: Statistics of surface air temperature observations in the Arctic. J. Climate.
Martin, S. and E.A. Munoz: Properties of the Arctic 2-Meter Air temperature field for 1979 to the present derived from a new gridded data set. J. Climate, 10, 1428-1440.
