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The Spring 2011 issue of The Earth Scientist is focused on modernizing seismology education. Thanks to IRIS, you can download this issue for free as a pdf. Print copies are available in our online store.

Climate Change: Regional Impacts

The concept of "global warming", as the words in the phrase clearly indicate, has a focus on changes in temperature and on changes that apply worldwide. Although changing temperatures are indeed the central feature of expected future climate change, other aspects of climate, such as precipitation rates, will be altered as well. Likewise, although global average temperatures are indeed expected to increase, temperatures and other aspects of climate change will not be evenly spread around our planet. Some place will warm much more than others; some regions will receive more rainfall, while others are exposed to more frequent droughts. Let's begin to look at aspects of climate change that occur on regional, instead of global, scales. Keep in mind that the science of making regional predictions of future climate is still quite new, and such predictions should be taken with a grain of salt. However, improving climate models and faster supercomputers are expected to help climate scientists make rapid advances in this evolving field, so regional climate projections should improve dramatically in coming years.

Here are some of the major elements of climate change that have a regional, instead of a global, influence.

Precipitation - too much? too little?

Projected precipitation changes

Projected changes in precipitation in 2100. Blue and green areas are expected to experience increases in precipitation. Yellow and pink areas are projected to have decreases.

The top image shows the period covering the months of December, January, and February. The bottom image covers June, July, and August.

Most high-latitude regions experience increased precipitation in both winter and summer. Most land areas, except for much of Asia, Greenland, and northern North America, are drier in the June through August timeframe. The pattern of precipitation on land in December through February is much more of a patchwork of mixed drier and moister regions.

Credits: Image courtesy of the IPCC (AR4 WG1 FAQ 11.1 page 127 Figure 1).

Global average precipitation is expected to rise by about 3% to 5% by the year 2100 in a range of scenarios considered in the IPCC's Fourth Assessment Report. This increase is not, however, expected to be distributed evenly around the globe or throughout the seasons in a given year.

Much of the increase in precipitation is expected to occur at high latitudes. Many regions near the equator and at mid-latitudes are expected to actually see decreases in precipitation. Increased snowfall near both poles may offset some of the melting of glaciers and ice sheets in these regions by adding fresh ice to the tops of these features. Some places in Antarctica are even gaining more snow via increased precipitation than they are losing to melting caused by rising temperatures.

Some of the increased rainfall is expected to come in the form of more frequent heavy downpours. Some regions may receive a net increase in rainfall; but the increase may manifest itself as heavier rains punctuated by longer dry spells between these deluges. This change in precipitation patterns is likely to cause greater incidence of flooding, especially in combination with land use changes such as deforestation.

Many areas, especially in low- and mid-latitude regions, are expected to suffer from more frequent and more severe droughts. Dry conditions, warmer temperatures that produce longer "fire seasons", and changes to ecosystems are expected to generate more and large wildfires in some areas.

Some presently dry regions may be glad to see increased rainfall, just as drier conditions may benefit some currently very wet places. However, heavy rainfall that causes flooding as well as extended or more frequent droughts are likely to be disruptive to ecosystems and agriculture in the afflicted regions.

Rising seas, coastlines, and islands

Not surprisingly, rising sea levels are expected to have adverse effects on coastal regions and islands worldwide.

Higher sea levels will hasten erosion of beaches and other types of terrain along the shoreline. Salty water will seep further inland in estuaries and brackish swamplands, altering ecosystems (many of which serve as nurseries for ocean-going fish and other aquatic creatures).

Some low-lying coastal regions will be subject to more frequent flooding or even permanent inundation. Large areas in the countries of Bangladesh and The Netherlands, along with the U.S. state of Florida, are only slightly above sea level, and thus are at great risk of even slight increases in sea level. Some small island nations in the Pacific are even in danger of being wiped off the map entirely as the water rises.

Hurricanes and other storms

Hurricane KatrinaHurricanes, typhoons, and other tropical cyclones are largely driven by energy from warm ocean waters. As the globe, including the oceans, warms, more energy is likely to be available for hurricanes. There is an active debate currently in progress in the community of scientists who study hurricanes as to how this warming may play out. Some scientists believe that global warming may not generate more hurricanes, but that it may produce a higher proportion of the strongest and most damaging storms. Some climate scientists believe this effect is already manifesting itself. Others claim that spotty records from years past, fluctuations caused by natural cycles, and variations between the various regions where hurricanes occur make it difficult to draw valid conclusions about current changes in hurricane activity.

Hurricanes currently occur in four major regions worldwide: the North Atlantic Ocean, the Northeastern Pacific, the Northwestern Pacific, and the Southwester Pacific/Indian Ocean. Each of these regions may be affected differently by changes to storm patterns caused by global warming. Hurricane seasons may start earlier and end later, providing more time for storms to occur. Storms may more frequently migrate away from their traditional tropical stomping grounds as warm waters move to higher latitudes, bringing tropical cyclones along for the ride. Hurricanes may form in places where they hadn't before; the unprecedented occurrence of Hurricane Catarina in the South Atlantic along the coast of Brazil in March 2004 may be an ominous portent of things to come.

Other aspects of climate change are likely to combine with hurricanes to produce further problems. The deadly storm surges that come ashore with hurricanes, causing extensive flooding and vast amounts of damage, will wash further inland as sea levels rise. Increased amounts of moisture in the atmosphere (caused by heightened evaporation rates brought on by higher temperatures) are likely to make for "wetter" hurricanes; flooding caused by extensive rainfall associated with hurricanes is therefore likely to be more common and severe.

Some scientists hypothesize that hurricanes play a critical role in Earth's overall climate by transporting heat from the warm tropics to the cooler high-latitude regions. If this is correct, a warmer planet may have a greater "need" for such transport, and an increase in hurricane frequency and/or intensity might be "required" to serve this "need". Hurricanes may not be the only beneficiaries of such an increase in available energy in the atmosphere; other types of storms may "have to" increase in frequency and/or severity to help dissipate this increased energy supply.

Mountain glaciers and water supplies

Mountain glaciers around the world are receding in most places, a trend that is likely to continue in the years ahead. Some regions are highly dependent on glaciers for their water supplies; meltwater from glaciers provides for agricultural and human consumption needs alike. Much of northern India gets water from Himalayan glaciers, while large portions of Chile relies on glaciers in the Andes for water. As glaciers shrink and in some places disappear, eventually these regions may become quite parched for lack of glacial meltwater.

High latitudes, North and South

Credits: Images courtesy the National Snow and Ice Data Center (NSIDC). Animation by Windows to the Universe staff (Randy Russell).

High latitude regions have experienced about twice as much warming as the global average, a trend that is expected to continue. The extent of sea ice in the Arctic Ocean has been decreasing rapidly; some models project complete loss of sea ice in the summertime in the Arctic by the middle of the 21st century. Melting glaciers and ice sheets in Antarctica and Greenland are contributing to sea level rise. A sudden collapse of either the Greenland of Antarctic ice sheet is considered unlikely (though not completely out of the question) in the short run, but would represent a huge "tipping point" problem that could drastically alter future climate quite suddenly should it occur.

Melting permafrost in the vast tundra is already disrupting wildlife and human activities. Permanently frozen tundra provides a solid platform for buildings, roadways, or seasonal migration routes for caribou. Seasonally melted, mushy tundra does not. Also, thawing tundra may generate many gigatons of methane gas. Methane is a powerful greenhouse gas, so such a release would only serve to exacerbate global warming.

Changes to large, regional climate/weather systems

Some large, cyclic or quasi-cyclic weather or climate systems may be disrupted by warming climates. The cycles of El Niņo and La Niņa events in the Pacific, or of seasonal monsoons in India and elsewhere may well be altered as the climate changes. Modeling of these systems even under "normal, natural" conditions is far from perfect, so predictions of their future behaviors as the climate warms are somewhat speculative. Disruptions of the normal patterns, particularly of the monsoons, could affect many millions of people in areas like India and Bangladesh. Many of those people are poor and cannot readily adapt their lifestyles to such changes; also, many of them are dependent on subsistence agriculture, which could be severely disrupted by changes to the monsoons.

El Niņo and La Niņa conditions also appear to have some influence on Atlantic hurricane formation and strengthening, so changes to these patterns could cause additional changes to hurricane patterns.

Changes to the Biosphere

While not strictly "climate", some regional changes to biological systems will be directly affected by climate changes, so we'll mention them briefly here.

As regional climates in various places warm and get wetter or drier, the ecosystems and various organisms that inhabit them are likely to undergo changes as well. Many tropical species will migrate towards the poles, as climates at higher latitude regions warm. Unfortunately, this includes certain invasive species and various types of pests. Certain diseases (such as malaria) and the creatures that transmit them which are currently confined to the tropics will be able to survive at higher latitudes.

Last modified April 18, 2008 by Randy Russell.

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The Summer 2010 issue of The Earth Scientist, available in our online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.

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