WHERE DO THE PRESIDENTIAL CANDIDATES STAND ON THE GLOBAL WARMING ISSUE?
I conducted a round table discussion on a message board with regard to global warming. Although there was not enough discourse about presidential candidates' standpoints on the critical issue, I found many points quite illuminating. Here are some summarizations of and links to the discussion. This was very enlightening!
Perspective 1:
Every once in a while, Al Gore and his buddies will say something like "support renewable energy!" "quit burning oil!" and "ride a bike/drive a prius!". Well, it turns out that we do need to do all of those things, but it's not because of global warming.
It's because of peak oil.
The issue is not one of oil "running out"; it's an issue of there not having enough to keep our economy running. This is because all oil production follows a bell curve. That's true whether we're talking about an individual field, a country, or on the planet as a whole.
Oil is increasingly plentiful on the upslope of the bell curve, increasingly scarce and expensive on the down slope. The peak of the curve coincides with the point at which the endowment of oil has been 50 percent depleted. Once the peak is passed, oil production begins to go down while cost begins to go up.
In practical terms, this means that if 2005 was the year of global Peak Oil, worldwide oil production in the 2030 will be the same as it was in 1980. However, the world’s population in 2030 will be both much larger and much more industrialized (oil-dependent) than it was in 1980. Consequently, worldwide demand for oil will outpace worldwide production of oil by a significant margin. As a result, the price will skyrocket, oil dependent economies will crumble, and resource wars will explode.
That's what we need to be worried about.
Perspective 2:
Once again, the issue is not running out of oil, it's that the declining production is not having enough to keep up with increasing demand.
FYI, American oil production peaked at 9.6 million barrels/day in 1970. Our oil production today is a little over half that amount today, and even drilling in ANWR won't get production back above 1970 levels:
http://tonto.eia.doe.gov/dnav/pet/hist/mcrfpus2a.htm
Perspective 3:
Civilization's last chance
The planet is nearing a tipping point on climate change, and it gets much worse, fast.
By Bill McKibben
May 11, 2008 New York Times.
Even for Americans -- who are constitutionally convinced that there will always be a second act, and a third, and a do-over after that, and, if necessary, a little public repentance and forgiveness and a Brand New Start -- even for us, the world looks a little terminal right now.
It's not just the economy: We've gone through swoons before. It's that gas at $4 a gallon means we're running out, at least of the cheap stuff that built our sprawling society. It's that when we try to turn corn into gas, it helps send the price of a loaf of bread shooting upward and helps ignite food riots on three continents. It's that everything is so tied together. It's that, all of a sudden, those grim Club of Rome types who, way back in the 1970s, went on and on about the "limits to growth" suddenly seem ... how best to put it, right.
All of a sudden it isn't morning in America, it's dusk on planet Earth.
There's a number -- a new number -- that makes this point most powerfully. It may now be the most important number on Earth: 350. As in parts per million of carbon dioxide in the atmosphere.
A few weeks ago, NASA's chief climatologist, James Hansen, submitted a paper to Science magazine with several coauthors. The abstract attached to it argued -- and I have never read stronger language in a scientific paper -- that "if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm."
Hansen cites six irreversible tipping points -- massive sea level rise and huge changes in rainfall patterns, among them -- that we'll pass if we don't get back down to 350 soon; and the first of them, judging by last summer's insane melt of Arctic ice, may already be behind us.
So it's a tough diagnosis. It's like the doctor telling you that your cholesterol is way too high and, if you don't bring it down right away, you're going to have a stroke. So you take the pill, you swear off the cheese, and, if you're lucky, you get back into the safety zone before the coronary. It's like watching the tachometer edge into the red zone and knowing that you need to take your foot off the gas before you hear that clunk up front.
In this case, though, it's worse than that because we're not taking the pill and we are stomping on the gas -- hard. Instead of slowing down, we're pouring on the coal, quite literally. Two weeks ago came the news that atmospheric carbon dioxide had jumped 2.4 parts per million last year -- two decades ago, it was going up barely half that fast.
And suddenly the news arrives that the amount of methane, another potent greenhouse gas accumulating in the atmosphere, has unexpectedly begun to soar as well. It appears that we've managed to warm the far north enough to start melting huge patches of permafrost, and massive quantities of methane trapped beneath it have begun to bubble forth.
And don't forget: China is building more power plants; India is pioneering the $2,500 car; and Americans are buying TVs the size of windshields, which suck juice ever faster.
Here's the thing. Hansen didn't just say that if we didn't act, there was trouble coming. He didn't just say that if we didn't yet know what was best for us, we'd certainly be better off below 350 ppm of carbon dioxide in the atmosphere.
His phrase was: "if we wish to preserve a planet similar to that on which civilization developed." A planet with billions of people living near those oh-so-floodable coastlines. A planet with ever-more vulnerable forests. (A beetle, encouraged by warmer temperatures, has already managed to kill 10 times more trees than in any previous infestation across the northern reaches of Canada this year. This means far more carbon heading for the atmosphere and apparently dooms Canada's efforts to comply with the Kyoto protocol, which was already in doubt because of its decision to start producing oil for the U.S. from Alberta's tar sands.)
We're the ones who kicked the warming off; now the planet is starting to take over the job. Melt all that Arctic ice, for instance, and suddenly the nice white shield that reflected 80% of incoming solar radiation back into space has turned to blue water that absorbs 80% of the sun's heat. Such feedbacks are beyond history, though not in the sense that Francis Fukuyama had in mind.
And we have, at best, a few years to short-circuit them -- to reverse course. Here's the Indian scientist and economist Rajendra Pachauri, who accepted the Nobel Prize on behalf of the Intergovernmental Panel on Climate Change last year (and, by the way, got his job when the Bush administration, at the behest of Exxon Mobil, forced out his predecessor): "If there's no action before 2012, that's too late. What we do in the next two to three years will determine our future. This is the defining moment."
In the next two or three years, the nations of the world are supposed to be negotiating a successor treaty to the Kyoto accord (which, for the record, has never been approved by the United States -- the only industrial nation that has failed to do so). When December 2009 rolls around, heads of state are supposed to converge on Copenhagen to sign a treaty -- a treaty that would go into effect at the last plausible moment to heed the most basic and crucial of limits on atmospheric CO2.
If we did everything right, Hansen says, we could see carbon emissions start to fall fairly rapidly and the oceans begin to pull some of that CO2 out of the atmosphere. Before the century was out, we might even be on track back to 350. We might stop just short of some of those tipping points, like the Road Runner screeching to a halt at the very edge of the cliff.
More likely, though, we're the coyote -- because "doing everything right" means that political systems around the world would have to take enormous and painful steps right away. It means no more new coal-fired power plants anywhere, and plans to quickly close the ones already in operation. (Coal-fired power plants operating the way they're supposed to are, in global warming terms, as dangerous as nuclear plants melting down.) It means making car factories turn out efficient hybrids next year, just the way U.S. automakers made them turn out tanks in six months at the start of World War II. It means making trains an absolute priority and planes a taboo.
It means making every decision wisely because we have so little time and so little money, at least relative to the task at hand. And hardest of all, it means the rich countries of the world sharing resources and technology freely with the poorest ones so that they can develop dignified lives without burning their cheap coal.
It's possible. The United States launched a Marshall Plan once, and could do it again, this time in relation to carbon. But at a time when the president has, once more, urged drilling in the Arctic National Wildlife Refuge, it seems unlikely. At a time when the alluring phrase "gas tax holiday" -- which would actually encourage more driving and more energy consumption -- has danced into our vocabulary, it's hard to see. And if it's hard to imagine sacrifice here, imagine China, where people produce a quarter as much carbon apiece as Americans do.
Still, as long as it's not impossible, we've got a duty to try to push those post-Kyoto negotiations in the direction of reality. In fact, it's about the most obvious duty humans have ever faced.
After all, those talks are our last chance; you just can't do this one lightbulb at a time.
We do have one thing going for us -- the Web -- which at least allows you to imagine something like a grass-roots global effort. If the Internet was built for anything, it was built for sharing this number, for making people understand that "350" stands for a kind of safety, a kind of possibility, a kind of future.
Hansen's words were well-chosen: "a planet similar to that on which civilization developed." People will doubtless survive on a non-350 planet, but those who do will be so preoccupied, coping with the endless unintended consequences of an overheated planet, that civilization may not.
Civilization is what grows up in the margins of leisure and security provided by a workable relationship with the natural world. That margin won't exist, at least not for long, as long as we remain on the wrong side of 350. That's the limit we face.
Bill McKibben, a scholar in residence at Middlebury College and the author, most recently, of "The Bill McKibben Reader," is the co-founder of Project 350 ( www.350.org ), devoted to reducing carbon dioxide in the atmosphere to 350 parts per million. A longer version of this article appears at Tomdispatch.com .
Perspective 4:
Stop being a follower and do some research.
Read about solar cycles and solar cycle 24 and sunspots.
We just exited a
Ice coverage went from record lows in 2007 to near average during the winter of 2008. All directly correlated with reduced sunspot activity.
From NOAA:
For the contiguous United States, the average temperature for March was 42°F (6°C), which was 0.4°F (0.2°C) below the 20th century mean.
March temperatures contrasted sharply with those in March 2007, when record breaking temperatures covered large parts of the nation during the last two weeks of the month.
The average temperature across both the contiguous U.S. and the globe during December 2007-February 2008 (climatological boreal winter) was the coolest since 2001, according to scientists at NOAA's National Climatic Data Center in Asheville, N.C.
Record Northern Hemisphere snow cover extent in January was followed by above average snow cover for the month of February.
* For the contiguous United States, the average temperature for April was 51.0°F (10.6°C), which was 1.0°F (0.6°C) below the 20th century mean and ranked as the 29th coolest April on record, based on preliminary data.
* On the Regional level, much of the U.S. experienced cooler than normal temperatures during April.
Mt. Crested Butte, Colorado received 418 inches (1061 cm) during the 2007-08 winter, breaking the previous record of 415 inches (1054 cm) from 1979-1980. Even Spokane, Washington was the second-snowiest on record with 89.5 inches (227 cm), four inches (10 cm) short of the previous record from 1949-1950.
Several cities and ski resorts across the country set new seasonal snowfall records during April. Madison, Wisconsin set a new seasonal record snow total of 101.4 inches (257.6 cm) on April 8, breaking the previous record of 76.1 inches (193.3 cm) from the 1978-79 season. Numerous ski resorts in the West reported record breaking snowfall this year, as did parts of northern Maine. Caribou, Maine received 197.8 inches (502 cm) of snowfall this winter, shattering the previous record of 181.1 inches (460 cm).
The February 2008 Southern Hemisphere sea ice extent was much above the 1979-2000 mean. This was the second largest sea ice extent in February (27% above the 1979-2000 mean) over the 30-year historical period, behind 2003. Sea ice extent for February has increased at a rate of 3.4%/decade.
Perspective 5:
Dalton Solar Minimum (1790 - 1820) global temperatures are lower than average.
Maunder Solar Minimum (1645 - 1715) coincident with the 'Little Ice Age'.
Sporer Solar Minimum (1420-1530) discovered by the analysis of radioactive carbon in tree rings that correlate with solar activity colder weather. Greenland settlements abandoned.
Wolf Solar Minimum (1280 - 1340) climate deterioration begins. Life gets harder in Greenland.
Medieval Solar Maximum (1075 - 1240) coincides with Medieval Warm Period. Vikings from Norway and Iceland found settlements in Greenland and North America.
Oort Solar Minimum (1010 - 1050) temperature on Earth is colder than average.
Perspective 6:
You are right - we will never run out of oil. But, it used to be that ole Jed would be shootin at some squirrels and texas tea came bubblin out of the ground. The best find in recent years was in the gulf of mexico, Jack 2. They found enough oil for two years worth of US consumption under 7,000 feet of water and 20,000 feet of rock.
Oil shale, oil sands, and coal are supposed to be our new saviors. They are all closer to the ground and we have mass quantities of the stuff - but refining it to a liquid we can put in our gas tanks is nasty and expensive. The only western country to ever use coal liquefication was Germany during WWII with slave labor.
Oil used to be cheap and plentiful - that's no longer true. The energy returned on energy invested (EROEI) on oil used to be 50-1. That is, you got 50 units of energy for every 1 unit you invested. It's now around 10-1 - and all other processes for putting gas in our tanks is far worse. Hydrogen is a net energy loser and corn ethanol is draws almost dead even.
So, the question is - how can we keep the same standard of living if the energy we use is both more expensive and less plentiful?
Perspective 7:
http://en.wikipedia.org/wiki/Global_warming
http://www.epa.gov/climatechange/
http://www.climatehotmap.org/
http://www.nrdc.org/globalwarming/Default.asp
This is from NOAA too.
Introduction
One of the most vigorously debated topics on Earth is the issue of climate change, and the National Environmental Satellite, Data, and Information Service (NESDIS) data centers are central to answering some of the most pressing global change questions that remain unresolved. The National Climatic Data Center contains the instrumental and paleoclimatic records that can precisely define the nature of climatic fluctuations at time scales of a century and longer. Among the diverse kinds of data platforms whose data contribute to NCDC's resources are: Ships, buoys, weather stations, weather balloons, satellites, radar and many climate proxy records such as tree rings and ice cores. The National Oceanographic Data Center contains the subsurface ocean data which reveal the ways that heat is distributed and redistributed over the planet. Knowing how these systems are changing and how they have changed in the past is crucial to understanding how they will change in the future. And, for climate information that extends from hundreds to thousands of years, paleoclimatology data, also available from the National Climatic Data Center, helps to provide longer term perspectives.
Internationally, the Intergovernmental Panel on Climate Change (IPCC), under the auspices of the United Nations (UN), World Meteorological Organization (WMO), and the United Nations Environment Program (UNEP), is the most senior and authoritative body providing scientific advice to global policy makers. The IPCC met in full session in 1990, 1995, 2001 and in 2007. They address issues such as the buildup of greenhouse gases, evidence, attribution, and prediction of climate change, impacts of climate change, and policy options.
Listed below are a number of questions commonly addressed to climate scientists, and brief replies (based on IPCC reports and other research) in common, understandable language. This list will be periodically updated, as new scientific evidence comes to light.
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1. What is the greenhouse effect, and is it affecting our climate?
The greenhouse effect is unquestionably real and helps to regulate the temperature of our planet. It is essential for life on Earth and is one of Earth's natural processes. It is the result of heat absorption by certain gases in the atmosphere (called greenhouse gases because they effectively 'trap' heat in the lower atmosphere) and re-radiation downward of some of that heat. Water vapor is the most abundant greenhouse gas, followed by carbon dioxide and other trace gases. Without a natural greenhouse effect, the temperature of the Earth would be about zero degrees F (-18°C) instead of its present 57°F (14°C). So, the concern is not with the fact that we have a greenhouse effect, but whether human activities are leading to an enhancement of the greenhouse effect by the emission of greenhouse gases through fossil fuel combustion and deforestation.
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2. Are greenhouse gases increasing?
Human activity has been increasing the concentration of greenhouse gases in the atmosphere (mostly carbon dioxide from combustion of coal, oil, and gas; plus a few other trace gases). There is no scientific debate on this point. Pre-industrial levels of carbon dioxide (prior to the start of the Industrial Revolution) were about 280 parts per million by volume (ppmv), and current levels are greater than 380 ppmv and increasing at a rate of 1.9 ppm yr-1 since 2000. The global concentration of CO2 in our atmosphere today far exceeds the natural range over the last 650,000 years of 180 to 300 ppmv. According to the IPCC Special Report on Emission Scenarios (SRES), by the end of the 21st century, we could expect to see carbon dioxide concentrations of anywhere from 490 to 1260 ppm (75-350% above the pre-industrial concentration).
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3. Is the climate warming?
Global surface temperatures have increased about 0.74°C (plus or minus 0.18°C) since the late-19th century, and the linear trend for the past 50 years of 0.13°C (plus or minus 0.03°C) per decade is nearly twice that for the past 100 years. The warming has not been globally uniform. Some areas (including parts of the southeastern U.S. and parts of the North Atlantic) have, in fact, cooled slightly over the last century. The recent warmth has been greatest over North America and Eurasia between 40 and 70°N. Lastly, seven of the eight warmest years on record have occurred since 2001 and the 10 warmest years have all occurred since 1995.
Recent analyses of temperature trends in the lower and mid- troposphere (between about 2,500 and 26,000 ft.) using both satellite and radiosonde (weather balloon) data show warming rates that are similar to those observed for surface air temperatures. These warming rates are consistent with their uncertainties and these analyses reconcile a discrepancy between warming rates noted on the IPCC Third Assessment Report (U.S. Climate Change Science Plan Synthesis and Assessment Report 1.1).
An enhanced greenhouse effect is expected to cause cooling in higher parts of the atmosphere because the increased "blanketing" effect in the lower atmosphere holds in more heat, allowing less to reach the upper atmosphere. Cooling of the lower stratosphere (about 49,000-79,500 ft.) since 1979 is shown by both satellite Microwave Sounding Unit and radiosonde data (see previous figure), but is larger in the radiosonde data likely due to uncorrected errors in the radiosonde data.
Relatively cool surface and tropospheric temperatures, and a relatively warmer lower stratosphere, were observed in 1992 and 1993, following the 1991 eruption of Mt. Pinatubo. The warming reappeared in 1994. A dramatic global warming, at least partly associated with the record El Niño, took place in 1998. This warming episode is reflected from the surface to the top of the troposphere.
There has been a general, but not global, tendency toward reduced diurnal temperature range (DTR: the difference between daily high or maximum and daily low or minimum temperatures) over about 70% of the global land mass since the middle of the 20th century. However, for the period 1979-2005 the DTR shows no trend since the trend in both maximum and minimum temperatures for the same period are virtually identical; both showing a strong warming signal. A variety of factors likely contribute to this change in DTR, particularly on a regional and local basis, including changes in cloud cover, atmospheric water vapor, land use and urban effects.
Indirect indicators of warming such as borehole temperatures, snow cover, and glacier recession data, are in substantial agreement with the more direct indicators of recent warmth. Evidence such as changes in glacial mass balance (the amount of snow and ice contained in a glacier) is useful since it not only provides qualitative support for existing meteorological data, but glaciers often exist in places too remote to support meteorological stations. The records of glacial advance and retreat often extend back further than weather station records, and glaciers are usually at much higher altitudes than weather stations, allowing scientists more insight into temperature changes higher in the atmosphere.
Large-scale measurements of sea-ice have only been possible since the satellite era, but through looking at a number of different satellite estimates, it has been determined that September Arctic sea ice has decreased between 1973 and 2007 at a rate of about -10% +/- 0.3% per decade. Sea ice extent for September for 2007 was by far the lowest on record at 4.28 million square kilometers, eclipsing the previous record low sea ice extent by 23%. Sea ice in the Antarctic has shown very little trend over the same period, or even a slight increase since 1979. Though extending the Antarctic sea-ice record back in time is more difficult due to the lack of direct observations in this part of the world.
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4. Are El Niños related to Global Warming?
El Niños are not caused by global warming. Clear evidence exists from a variety of sources (including archaeological studies) that El Niños have been present for thousands, and some indicators suggest maybe millions, of years. However, it has been hypothesized that warmer global sea surface temperatures can enhance the El Niño phenomenon, and it is also true that El Niños have been more frequent and intense in recent decades. Whether El Niño occurrence changes with climate change is a major research question.
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5. Is the hydrological cycle (evaporation and precipitation) changing?
Globally-averaged land-based precipitation shows a statistically insignificant upward trend with most of the increase occurring in the first half of the 20th century. Further, precipitation changes have been spatially variable over the last century. On a regional basis increases in annual precipitation have occurred in the higher latitudes of the Northern Hemisphere and southern South America and northern Australia. Decreases have occurred in the tropical region of Africa, and southern Asia. Due to the difficulty in measuring precipitation, it has been important to constrain these observations by analyzing other related variables. The measured changes in precipitation are consistent with observed changes in stream flow, lake levels, and soil moisture (where data are available and have been analyzed).
Northern Hemisphere snow cover extent has consistently remained below average since 1987, and has decreased by about 10% since 1966. This is mostly due to a decrease in spring and summer snow extent over both the Eurasian and North American continents since the mid-1980s. Winter and autumn snow cover extent have shown no significant trend for the northern hemisphere over the same period.
Clouds are also an important indicator of climate change. Surface-based observations of cloud cover suggest increases in total cloud cover over many continental regions. This increase since 1950 is consistent with regional increases in precipitation for the same period. However, global analyses of cloud cover over land for the 1976-2003 period show little change.
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6. Is the atmospheric/oceanic circulation changing?
A rather abrupt change in the El Niño - Southern Oscillation behavior occurred around 1976/77. Often called the climatic shift of 1976/77, this new regime has persisted. There have been relatively more frequent and persistent El Niño episodes rather than the cool episode La Niñas. This behavior is highly unusual in the last 130 years (the period of instrumental record). Changes in precipitation over the tropical Pacific are related to this change in the El Niño - Southern Oscillation, which has also affected the pattern and magnitude of surface temperatures. However, it is unclear as to whether this apparent change in the ENSO cycle is related to global warming.
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7. Is the climate becoming more variable or extreme?
Examination of changes in climate extremes requires long-term daily or even hourly data sets which until recently have been scarce for many parts of the globe. However these data sets have become more widely available allowing research into changes in temperature and precipitation extremes on global and regional scales. Global changes in temperature extremes include decreases in the number of unusually cold days and nights and increases in the number of unusually warm days and nights. Other observed changes include lengthening of the growing season, and decreases in the number of frost days.
Global temperature extremes have been found to exhibit no significant trend in interannual variability, but several studies suggest a significant decrease in intra-annual variability. There has been a clear trend to fewer extremely low minimum temperatures in several widely-separated areas in recent decades. Widespread significant changes in extreme high temperature events have not been observed. There is some indication of a decrease in day-to-day temperature variability in recent decades.
In areas where a drought or excessive wetness usually accompanies an El Niño or La Niña, these dry or wet spells have been more intense in recent years. Further, there is some evidence for increasing drought worldwide, however in the U.S. there is no evidence for increasing drought.In some areas where overall precipitation has increased (ie. the mid-high northern latitudes), there is evidence of increases in the heavy and extreme precipitation events. Even in areas such as eastern Asia, it has been found that extreme precipitation events have increased despite total precipitation remaining constant or even decreasing somewhat. This is related to a decrease in the frequency of precipitation in this region.
Many individual studies of various regions show that extra-tropical cyclone activity seems to have generally increased over the last half of the 20th century in the northern hemisphere, but decreased in the southern hemisphere. Furthermore, hurricane activity in the Atlantic has shown an increase in number since 1970 with a peak in 2005. It is not clear whether these trends are multi-decadal fluctuations or part of a longer-term trend.
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8. How important are these changes in a longer-term context?
Paleoclimatic data are critical for enabling us to extend our knowledge of climatic variability beyond what is measured by modern instruments. Many natural phenomena are climate dependent (such as the growth rate of a tree for example), and as such, provide natural 'archives' of climate information. Some useful paleoclimate data can be found in sources as diverse as tree rings, ice cores, corals, lake sediments (including fossil insects and pollen data), speleothems (stalactites etc), and ocean sediments. Some of these, including ice cores and tree rings provide us also with a chronology due to the nature of how they are formed, and so high resolution climate reconstruction is possible in these cases. However, there is not a comprehensive 'network' of paleoclimate data as there is with instrumental coverage, so global climate reconstructions are often difficult to obtain. Nevertheless, combining different types of paleoclimate records enables us to gain a near-global picture of climate changes in the distant past.
For Northern Hemisphere temperature, recent decades appear to be the warmest since at least about 1000AD, and the warming since the late 19th century is unprecedented over the last 1000 years. Older data are insufficient to provide reliable hemispheric temperature estimates. Ice core data suggest that the 20th century has been warm in many parts of the globe, but also that the significance of the warming varies geographically, when viewed in the context of climate variations of the last millennium.
Large and rapid climatic changes affecting the atmospheric and oceanic circulation and temperature, and the hydrological cycle, occurred during the last ice age and during the transition towards the present Holocene period (which began about 10,000 years ago). Based on the incomplete evidence available, the projected change of 3 to 7°F (1.5 - 4°C) over the next century would be unprecedented in comparison with the best available records from the last several thousand years.
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9. Is sea level rising?
Global mean sea level has been rising at an average rate of 1.7 mm/year (plus or minus 0.5mm) over the past 100 years, which is significantly larger than the rate averaged over the last several thousand years. Depending on which greenhouse gas increase scenario is used (high or low) projected sea-level rise is projected to be anywhere from 0.18 (low greenhouse gas increase) to 0.59 meters for the highest greenhouse gas increase scenario. However, this increase is due mainly to thermal expansion and contributions from melting alpine glaciers, and does not include any potential contributions from melting ice sheets in Greenland or Antarctica. Larger increases cannot be excluded but our current understanding of ice sheet dynamics renders uncertainties too large to be able to assess the likelihood of large-scale melting of these ice sheets.
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10. Can the observed changes be explained by natural variability, including changes in solar output?
Since our entire climate system is fundamentally driven by energy from the sun, it stands to reason that if the sun's energy output were to change, then so would the climate. Since the advent of space-borne measurements in the late 1970s, solar output has indeed been shown to vary. With now 28 years of reliable satellite observations there is confirmation of earlier suggestions of an 11 (and 22) year cycle of irradiance related to sunspots but no longer term trend in these data. Based on paleoclimatic (proxy) reconstructions of solar irradiance there is suggestion of a trend of about +0.12 W/m2 since 1750 which is about half of the estimate given in the last IPCC report in 2001. There is though, a great deal of uncertainty in estimates of solar irradiance beyond what can be measured by satellites, and still the contribution of direct solar irradiance forcing is small compared to the greenhouse gas component. However, our understanding of the indirect effects of changes in solar output and feedbacks in the climate system is minimal. There is much need to refine our understanding of key natural forcing mechanisms of the climate, including solar irradiance changes, in order to reduce uncertainty in our projections of future climate change.
In addition to changes in energy from the sun itself, the Earth's position and orientation relative to the sun (our orbit) also varies slightly, thereby bringing us closer and further away from the sun in predictable cycles (called Milankovitch cycles). Variations in these cycles are believed to be the cause of Earth's ice-ages (glacials). Particularly important for the development of glacials is the radiation receipt at high northern latitudes. Diminishing radiation at these latitudes during the summer months would have enabled winter snow and ice cover to persist throughout the year, eventually leading to a permanent snow- or icepack. While Milankovitch cycles have tremendous value as a theory to explain ice-ages and long-term changes in the climate, they are unlikely to have very much impact on the decade-century timescale. Over several centuries, it may be possible to observe the effect of these orbital parameters, however for the prediction of climate change in the 21st century, these changes will be far less important than radiative forcing from greenhouse gases.
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11. What about the future?
Due to the enormous complexity of the atmosphere, the most useful tools for gauging future changes are 'climate models'. These are computer-based mathematical models which simulate, in three dimensions, the climate's behavior, its components and their interactions. Climate models are constantly improving based on both our understanding and the increase in computer power, though by definition, a computer model is a simplification and simulation of reality, meaning that it is an approximation of the climate system. The first step in any modeled projection of climate change is to first simulate the present climate and compare it to observations. If the model is considered to do a good job at representing modern climate, then certain parameters can be changed, such as the concentration of greenhouse gases, which helps us understand how the climate would change in response. Projections of future climate change therefore depend on how well the computer climate model simulates the climate and on our understanding of how forcing functions will change in the future.
The IPCC Special Report on Emission Scenarios determines the range of future possible greenhouse gas concentrations (and other forcings) based on considerations such as population growth, economic growth, energy efficiency and a host of other factors. This leads a wide range of possible forcing scenarios, and consequently a wide range of possible future climates.
According to the range of possible forcing scenarios, and taking into account uncertainty in climate model performance, the IPCC projects a best estimate of global temperature increase of 1.8 - 4.0°C with a possible range of 1.1 - 6.4°C by 2100, depending on which emissions scenario is used. However, this global average will integrate widely varying regional responses, such as the likelihood that land areas will warm much faster than ocean temperatures, particularly those land areas in northern high latitudes (and mostly in the cold season). Additionally, it is very likely that heat waves and other hot extremes will increase.
Precipitation is also expected to increase over the 21st century, particularly at northern mid-high latitudes, though the trends may be more variable in the tropics, with much of the increase coming in more frequent heavy rainfall events. However, over mid-continental areas summer-drying is expected due to increased evaporation with increased temperatures, resulting in an increased tendency for drought in those regions.
Snow extent and sea-ice are also projected to decrease further in the northern hemisphere, and glaciers and ice-caps are expected to continue to retreat.
Unimpressed by Tuesday primary numbers, U.S. Rep. Pete Visclosky announced his endorsement of