Global Warming - Evidence

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level. IPCC 2007

Changes in Air Temperature Over the Past 400,000 Years Temperature deduced from isotopic analysis of Antarctic ice cores. An ice core is a sample from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods. The composition of these ice cores, especially the presence of hydrogen and oxygen isotopes, provides a picture of the climate at the time. Because water molecules containing heavier isotopes have a lower vapor pressure, when the temperature falls, the heavier water molecules condense faster than the normal water molecules. The relative concentrations of the heavier isotopes in the condensate indicate the temperature at the time.

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Eleven of the last twelve years ( ) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). In the last 100 years we’ve gained 0.74 °C. The warming trend over the last 50 years (0.13 °C per decade) is nearly twice that for the last 100 years.

Loss of glaciers

Comparison photos showing the decline of Pedersen Glacier in Kenai Fjords National Park, Alaska.

Comparison photos of Muir and Riggs Glaciers in Glacier Bay National Park and Preserve, Alaska. Muir glacier, parts of which were greater than 65 meters thick in 1941, has retreated out of the image in 2004 (towards the upper left). The distance to the visible Riggs glacier in 2004 is ~3 km. During this time, the Muir Glacier retreated more than 20 km (Benson and Field 1995).

Whitechuck glacier Washington About

This image shows the termini of the glaciers in the Bhutan-Himalaya. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. There is a strong correlation between increasing temperatures and glacial retreat in this region.

The loss of glaciers is a general, not isolated, phenomenon that has been accelerating in recent years.

The Greenland icecap contains 1/8th of the total global ice-mass.

The Greenland icecap is rapidly thinning at lower elevations Recently, fears have grown that continued global warming will make the Greenland Ice Sheet cross a threshold where long-term melting of the ice sheet is inevitable. If the entire 2.85 million km³ of ice were to melt, global sea levels would rise 7.2 m (23.6 ft)

Surface river of meltwater on the Greenland icecap plunging into a vertical chute.

An area of Arctic sea ice the size of Florida has melted away in just the last six days as melting at the top of the planet continues at a record rate. - ABC News 9/10/2007

Arctic Sea ice reached record lows in September, The Northwest Passage opened for the first time during satellite recordings.

This satellite image shows the 2002 breakup of the Larsen B Ice Shelf in comparison of the US state of Rhode Island. This region, covering approximately 3250 km 2 with 200 meter thick ice, had been continuously glaciated since before the end of the last glacial period (Domack et al. 2005).

On February 28, 2008 a part of the Wilkins Ice Shelf collapsed and was “hanging by a thread”. This area is about three times the area of Manhattan.

Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 20 centimeters per century (2 mm/year).

In 1896, a Swedish chemist, Svante Arrhenius predicted that changes in CO2 concentration could substantially alter the surface temperature of the earth through the greenhouse effect. Although the motivation for his work was an explanation of the ice ages, he did predict that human emissions of CO2 would lead to global warming, though he thought that would be a positive change. His ideas were not generally accepted, in part because there was not enough understanding of the climate and the effects of photosynthesis and absorption of CO2 into the oceans. CO2 and Global Warming

Greenhouse gases like carbon dioxide, water and methane naturally blanket the Earth and keep it about 33° C warmer than it would be without these gases in the atmosphere. This is called the green house effect. Light from the sun is not absorbed by these gases, but a portion of the heat coming from the surface of the earth is absorbed by the gases and reradiated in all directions, trapping some of the heat in our atmosphere.

In 1896, a Swedish chemist, Svante Arrhenius predicted that changes in CO2 concentration could substantially alter the surface temperature of the earth through the greenhouse effect. Although the motivation for his work was an explanation of the ice ages, he did predict that human emissions of CO2 would lead to global warming, though he thought that would be a positive change. His ideas were not generally accepted, in part because there was not enough understanding of the climate and the effects of photosynthesis and absorption of CO2 into the oceans. CO2 and Global Warming

Keeling’s accurate measurements over the last 50 years demonstrated that CO2 concentrations were actually increasing as Arrhenius had predicted.

* Global atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values over the past 650,000 years - IPCC, 2007

Variations in CO 2 concentration in the atmosphere during the last 400 thousand years as measured from ice cores. Since the Industrial Revolution, circa 1800, the burning of fossil fuels has caused a dramatic increase of CO2 in the atmosphere, reaching levels which are likely unprecedented in the last 20 million years [1]. This increase has been implicated as a primary cause of global warming.

The timescales for removal of emitted carbon dioxide from the atmosphere. Mixing in the biosphere and oceans removes 70-85% of emissions after 200 years, but the remainder establishes a new equilibrium that may persist for hundreds of thousands of years.

* Anthropogenic warming and sea level rise will continue for centuries even if greenhouse gas concentrations are stabilized. Climate Change Summary * Warming of the climate system is unequivocal. * Most of the increase in global temperatures since the mid-20th century is due to the increased concentration of anthropogenic greenhouse gases. * There will probably be an increase in droughts, tropical cyclones and extreme high tides (>66% chance). Slightly edited from IPCC 2007 * There will likely be more frequent warm spells, heat waves and heavy rainfall (>90% chance). * Sea levels will probably rise by 18 to 59 cm (7.08 to in). * World temperatures will rise by 1.1 and 6.4 °C during the 21st century. * The probability that this is caused by natural climatic processes alone is less than 5%.