Scientists can argue all they want about how many degrees the planet is warming and what the trend portends, but meanwhile earth's plants, insects and animals are not waiting for the outcome. They are already adjusting their patterns of behavior.
One of the surest barometers of the warming climate is the response of the non-human natural world to changing conditions, and biologists who study the responses have been aware for some years that the biosphere is acknowledging global warming.
Nina Leopold Bradley, a plant ecologist and daughter of the conservation pioneer Aldo Leopold, published a 1999 paper in the Proceedings of the National Academy of Sciences on her 61-year uninterrupted phenological records. Phenology studies an organism's development and life cycle.
Bradley's record of 300 phenophases found that even prior to 1999, spring was arriving in higher latitudes several weeks earlier than in the earlier years of her data. Birds arrived sooner on their migrations from the south and plants flowered earlier. The Eastern phoebe is showing up about 20 days before it used to. The forest phlox is blooming in late April instead of mid-May. Half of the 300 phenophases Leopold tracked showed a response consistent with warming.
In England, the cuckoo returns earlier. An analysis of 65 bird species in the United Kingdom shows about one-third are laying their eggs four to seven days earlier than they did 25 years ago.
"One of the major, most well-documented and robust findings in ecology over the past century has been the crucial role of climate in determining the geographical distribution of species and ecological communities," concluded a report titled "Observed Impacts of Global Climate Change in the United States," released by the Pew Center on Global Climate last week.
Pew researchers looked at about 40 studies that could provide an assessment of whether climate was affecting biology.
"Half of the studies provide strong evidence of a causal link between the biological change and climate change," said Camille Parmesan, a University of Texas-Austin biologist and one of the world's leading experts on this issue.
These changes are occurring across all species, Parmesan said.
Parmesan has spent much of her career studying the checkerspot butterfly, which migrates between Mexico and southern California. Some localized extinctions already have occurred across some of its habitat.
"There have been large numbers of population extinctions in Mexico and southern California in areas where the habitat is still acceptable."
According to Parmesan's earlier studies, one extinction event was triggered when a checkerspot population migrated north prematurely, relying on a warming temperature signal, then was caught in a severe snowstorm in its northern habitat.
Throughout the United States, she said, "spring is about two weeks earlier. Tree swallows are nesting nine days earlier. Tropical species have moved up to Florida and the Gulf Coast. Bird and butterfly watchers are seeing many, many new species coming up from Mexico and the Caribbean."
The report also found alterations of ecosystem processes such as carbon cycling and storage. The Alaskan tundra, for instance, has switched from being a net sink of carbon dioxide - absorbing and storing more carbon from the atmosphere than it releases - to "being a net source of CO2, because warmer winters have allowed dead plant matter previously stored in the soil to decompose and release CO2."
The Pew report coincided with the release in Iceland of the "Arctic Climate Impact Assessment (ACIA)," which stated that the impacts of global warming were affecting people in the Arctic.
"The Arctic is experiencing some of the most rapid and severe climate changes on Earth," said ACIA chairman Robert Corell.
The ACIA found Arctic winter temperatures have increased from 4 to 7 degrees Fahrenheit in the last 50 years and should go up about twice that much in the next 100 years.
Arctic summer sea ice will decline by 50 percent by the end of the twenty-first century, the assessment found, with some models predicting complete disappearance of summer sea ice.
"Should the Arctic Ocean become ice-free in summer, it is likely that polar bears and some seal species would be driven toward extinction," the report concluded.
However, another report, "The Impacts of Climate Change: An Appraisal for the Future," completed by the Britain-based International Policy Network (IPN), paints a rosier picture.
"A warming of the magnitude predicted is more likely than not to be beneficial to the fisheries of the North Atlantic," the IPN report said.
The important commercial species that probably would benefit from warming include cod, haddock, saithe, herring, blue whiting and several types of flatfish and crustaceans - such as the Norway lobster.
In a limited economic sense the IPN report can argue warming might be a good thing. The problem is whether one cares what happens to the polar bears, checkerspot butterflies and other unconsumables.
The Pew researchers tried to transcend the economic argument. They assumed a value - unspecified - for noncommercial species, and in doing so rendered the warming news less optimistic.
This tug-of-war over calculating economic values is the one that ultimately will have to be decided by humans, because animals and plants can adjust only so much.
"When dandelions have set the mark of May on Wisconsin pastures, it is time to listen for the final proof of spring," wrote Aldo Leopold in A Sand County Almanac."
"Sit down on a tussock, cock your ears at the sky, dial out the bedlam of meadowlarks and redwings, and soon you may hear it: the flight of the upland plover, just now back from the Argentine."
Or maybe not.