Oceans
Sea Level Rise
As the average global temp rises the water in the oceans expand and the ice caps start to melt which adds more to the volume of expanding ocean water. From 3,000 years ago to the 1900's, the sea level had remained mostly constant. But from 1900 to 1992 the sea level has risen 1-2 mm/yr, and from 1992 until now it has risen about 3 mm/yr.
According to James Hansen, melting at the poles is not neat and orderly; rather it changes suddenly. For instance a temperature change of 2-3 degrees does not give the same results it would have given millions of years ago when the water rose only 59 centimeters. Today that same temperature change would cause a sea level rise of 25 meters because the ice responded more quickly to the rise in temperature! (Hansen, James. paper. 18 May 2007)
Temperature Rise
The temperature of the Antarctic Southern Ocean rose by 0.17 °C (0.31 °F) between the 1950s and the 1980s, nearly twice the rate for the world's oceans as a whole. As well as effects on ecosystems (e.g. by melting sea ice, affecting algae that grow on its underside), warming could reduce the ocean's ability to absorb CO2. More important for the United States may be the temperature rise in the Gulf of Mexico. As hurricanes cross the warm Loop Current coming up from South America, they can gain great strength in under a day (as did Hurricane Katrina and Hurricane Rita in 2005), with water above 85 °F seemingly promoting Category 5 storms. Hurricane season ends in November as the waters cool.
Acidification
The world’s oceans soak up much of the carbon dioxide produced by living organisms, either as dissolved gas, or in the skeletons of tiny marine creatures that fall to the bottom to become chalk or limestone. Oceans currently absorb about one tonne of CO2 per person per year. It is estimated that the oceans have absorbed around half of all CO2 generated by human activities since 1800 (120,000,000,000 tonnes or 120 pentagrams of carbon). But in water, carbon dioxide becomes a weak carbonic acid, and the increase in the greenhouse gas since the industrial revolution has already lowered the average pH (the laboratory measure of acidity) of seawater by 0.1 units, to 8.2. Predicted emissions could lower it by a further 0.5 by 2100, to a level not seen for millions of years. There are concerns that increasing acidification could have a particularly detrimental effect on corals (16% of the world's coral reefs have died from bleaching caused by warm water in 1998, which coincidentally was the warmest year ever recorded) and other marine organisms with calcium carbonate shells. Increased acidity may also directly affect the growth and reproduction of fish as well as the plankton on which they rely for food.
Shutdown of Thermohaline Circulation
There is some speculation that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would affect in particular areas like Scandinavia and Britain that are warmed by the North Atlantic drift. More significantly, it could lead to an oceanic anorexic event. The chances of this near-term collapse of the circulation are unclear; there is some evidence for the short-term stability of the Gulf Stream and possible weakening of the North Atlantic drift. However, the degree of weakening, and whether it will be sufficient to shut down the circulation, is under debate. As yet, no cooling has been found in northern Europe or nearby seas.
Ecosystems
"The global temperatures predicted for the coming centuries may trigger a new ‘mass extinction event’, where over 50 per cent of animal and plant species would be wiped out." (scientists from University of York)
Rising temperatures are beginning to have a noticeable impact on birds. Increasing global temperature means that ecosystems will change; some species are being forced out of their habitats (possibly to extinction) because of changing conditions, while others are flourishing.
Few of the terrestrial ecoregions on Earth could expect to be unaffected. Arctic and Antarctic fauna such as polar bears, emperor penguins, gyrfalcons, and snowy owls that prey on lemmings will be hurt by loss of snow and cold weather.
Marine invertebrates enjoy peak growth at the temperatures they have adapted to, regardless of how cold these may be, and cold-blooded animals found at greater latitudes and altitudes generally grow faster to compensate for the short growing season. Warmer-than-ideal conditions result in higher metabolism and consequent reductions in body size despite increased foraging, which in turn elevates the risk of predation. Indeed, even a slight increase in temperature during development impairs growth efficiency and survival rate in rainbow trout.
Butterflies have shifted their ranges northward by 200 km in Europe and North America. Plants lag behind, and larger animals' migration is slowed down by cities and highways. In Britain, spring butterflies are appearing an average of 6 days earlier than two decades ago.
In the Arctic, the waters of Hudson Bay are ice-free for three weeks longer than they were thirty years ago, affecting polar bears, which prefer to hunt on sea ice.
Two 2002 studies in Nature (vol 421) surveyed the scientific literature to find recent changes in range or seasonal behaviour by plant and animal species. Of species showing recent change, 4 out of 5 shifted their ranges towards the poles or higher altitudes, creating "refugee species".
Frogs were breeding, flowers blossoming and birds migrating an average 2.3 days earlier each decade; butterflies, birds and plants moving towards the poles by 6.1 km per decade.
A 2005 study concludes human activity is the cause of the temperature rise and resultant changing species behaviour, and links these effects with the predictions of climate models to provide validation for them.
Mechanistic studies have documented extinctions due to recent climate change: McLaughlin et al. documented two populations of Bay checkerspot butterfly being threatened by precipitation change. Parmesan states, "Few studies have been conducted at a scale that encompasses an entire species" and McLaughlin et al. agreed "few mechanistic studies have linked extinctions to recent climate change." Daniel Botkin and other authors in one study believe that projected rates of extinction are overestimated.
Forests
Pine forests in British Columbia have been devastated by a pine beetle infestation, which has expanded unhindered since 1998 at least in part due to the lack of severe winters since that time; a few days of extreme cold kill most mountain pine beetles and have kept outbreaks in the past naturally contained.
The infestation, which will have killed 50% of the lodgepole pines by 2008 has passed to Alberta and will spread further East and eventually into America given continued milder winters.
Besides the immediate ecological and economic impact, the huge dead forests provide a fire risk as well. Forests in some regions potentially face an increased risk of forest fires. The 10-year average of boreal forest burned in North America, after several decades of around 10,000 km² (2.5 million acres), has increased steadily since 1970 to more than 28,000 km² (7 million acres) annually. This change may be due in part to changes in forest management practices.
In the western U. S., since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has been reported in Canada from 1920 to 1999. Also note forest fires since 1997 in Indonesia. The fires are started to clear forest for agriculture. These occur from time to time and can set fire to the large peat bogs in that region. The CO2 released by these peat bog fires has been estimated, in an average year, to release 15% of the quantity of CO2 produced by fossil fuel combustion.
Ecological Productivity
Increasing average temperature and carbon dioxide may have the effect of improving ecosystems' productivity.
In photo respiration, carbon dioxide that oxygen can enter a plant's chloroplasts and take the place of carbon dioxide in the Calvin cycle. This causes the sugars being made to be destroyed, suppressing growth.
Higher carbon dioxide concentrations tend to reduce photo respiration. Satellite data shows that the productivity of the northern hemisphere has increased since 1982 (although attribution of this increase to a specific cause is difficult).
IPCC models predict that higher CO2 concentrations would only spur growth of flora up to a point, because in many regions the limiting factors are water or nutrients, not temperature or CO2; after that, greenhouse effects and warming would continue but there would be no compensatory increase in growth.
Research done by the Swiss Canopy Crane Project suggests that slow-growing trees only are stimulate
d in growth for a short period under higher CO2 levels, while faster growing plants like Liana benefit in the long term.In general, but especially in rain forests, this means that Liana become the prevalent species; and because they decompose much faster than trees their carbon content is more quickly returned to the atmosphere. Slow growing trees incorporate atmospheric carbon for decades.
