Objection: A few glaciers receding today is not proof of global warming. Glaciers have grown and receded differently in many times and places.
Answer: Firstly, it is more than “a few glaciers” that are receding; it is a pervasive, sustained, and accelerating global trend. The National Snow and Ice Data Centre (NSIDC) maintains a chart of global glacier mass balance, and for as far back as their data allows us to look, all but a few years have shown a loss in ice volume of subpolar and mountain glaciers. Further, annual losses are increasing.
But no one claims that melting glaciers are proof of global warming. Proof is a mathematical concept. In climate science one needs to look at the balance of evidence. The above data is just one piece of evidence that is consistent with global warming.
So what do we find if we look to the other aspects of the cryosphere? It turns out what we find is lots more evidence indicative of world-wide and sustained temperature increases:
- Sea ice in the arctic is reaching new record declines as the year 2006 continues the pattern of sharply decreasing Arctic sea ice.
- Recent measurements by NASA have found that Greenland’s massive ice sheet has been losing nearly 100 gigatons of ice annually in recent years.
- Glaciers in Greenland are receding and calving at record rates.
- Ancient permafrost is also thawing (which represents its own dangers).
And of course, this is all consistent with all the other evidence of warming out there. Clearly we are dealing with much more than a few receding glaciers.