The Most Common Skeptical Arguments About Climate Change (from the Grist articles: How to Talk to a Climate Skeptic – see site for images)
Glaciers have always grown and receded
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.
But the glaciers are not melting
Objection: Sure, some glaciers are melting. But if you look at the studies, most of those for which we have data are growing.
Answer: This is simply not true, rumors on “the internets” aside. The National Snow and Ice Data Centre and their State of the Cryosphere division, on their Glacial Balance page, report an overall accelerating rate of glacial mass loss. The World Glacier Monitoring Service has similar findings, the most recent data coming from 2004.
While there surely are some growing glaciers, studies like these are designed to determine a global trend by ensuring glaciers from all regions of the globe are assessed. There are 67,000 glaciers in the World Glacier Inventory. Not all, or even most, have quality data for many decades, but there are enough with adequate data, located in enough regions of the globe, to know the average trend.
Don’t forget: there is similar evidence from other parts of the cryosphere. It’s also worth noting that given the right circumstances, warming can actually cause glacier growth, with accumulation of increased winter snowfall outweighing increased summer melting.
Check this page for some good before-and-after images of glaciers over the last century, as well as other images of visible effects of global warming. There are also some compelling animations of changes in Glacier Bay National Park here.
Antarctic sea ice is increasing
Objection: Sure, sea ice is shrinking in the Arctic, but it is growing in the Antarctic. Sounds like natural fluctuations that balance out in the end.
Answer: Overall, it is true that sea ice in the Antarctic is increasing.
Around the peninsula, where there is a lot of warming [PDF], the ice is retreating. This is the area of the recent and dramatic Larsen B and Ross ice shelf breakups.
But the rest of the continent has not shown any clear warming or cooling and sea ice has increased over the last decade or so.
This is not actually a big surprise.
In fact, it is completely in line with model expectations that CO2-dominated forcing will have a disproportionately large effect in the north. The reasons lie in the much larger amount of land in the northern hemisphere and the fact that the ocean’s thermal inertia and ability to mix delay any temperature signal from the ongoing absorption of heat. The local geography also plays a dominating role. The circumpolar current acts as a buffer preventing warm water from the tropics from transporting heat to the South Pole, a buffer that does not exist in the north. You can read some more details about that here.
Does it “balance out” in the end? Not really. Sea ice in the Arctic is reaching dramatic record lows. There are other components of the cryosphere that we can look at as well, permafrost, the Greenland ice sheet, global glacier mass, and these all carry the Global Warming signal.
One must look at the balance of evidence, not just those bits one likes. And this balance is clearly in agreement with all other indicators that warming is real and rapid.
Antarctic ice is growing
Objection: The Antarctic ice sheets are actually growing, which wouldn’t be happening if global warming were real.
Answer: There are two distinct problems with this argument.
First, any argument that tries to use a regional phenomenon to disprove a global trend is dead in the water. Anthropogenic global warming theory does not predict uniform warming throughout the globe. We need to assess the balance of the evidence.
In the case of this particular region, there is actually very little data about the changes in the ice sheets. The growth in the East Antarctic ice sheet indicated by some evidence is so small, and the evidence itself so uncertain, the sheet may well be shrinking.
But even this weak piece of evidence may no longer be current. Some recent results from NASA’s GRACE experiment, measuring the gravitational pull of the massive Antarctic ice sheets, have indicated that on the whole, ice mass is being lost.
Second, ice-sheet thickening is not inconsistent with warming! Warmer climates tend toward more precipitation. The Antarctic is one of the most extreme deserts on the planet. As it warms, we would expect it to receive more snow. But even a whopping warming of 20 degrees — say, from -50 degrees C to -30 degrees C — would still leave it below freezing, so the snow wouldn’t melt. Thus, an increase in ice mass.
While on the subject of ice sheets: Greenland is also growing ice in the center, for the same reasons described above. But it is melting on the exterior regions, on the whole losing approximately 200 km3 of ice annually, doubled from just a decade ago. This is a huge amount compared to changes in the Antarctic — around three orders of magnitude larger. So in terms of sea-level rise, any potential mitigation due to East Antarctic Ice Sheet growth is wiped out many times over by Greenland’s melting.
Greenland used to be green
Objection: When the Vikings settled it, Greenland was a lovely, hospitable island, not the frozen wasteland it is today. It was not until the Little Ice Age that it got so cold they abandoned it.
Answer: First, Greenland is part of a single region. It can not be necessarily taken to represent a global climate shift. See the post on the Medieval Warm Period for a global perspective on this time period. Briefly, the available proxy evidence indicates that global warmth during this period was not particularly pronounced, though some regions may have experienced greater warming than others.
Second, a quick reality check shows that Greenland’s ice cap is hundreds of thousands of years old and covers over 80% of the island. The vast majority of land not under the ice sheet is rock and permafrost in the far north. How different could it have been just 1,000 years ago?
Below is a brief account of the Viking settlement, based on Jared Diamond’s “Collapse”.
Greenland was called Greenland by Erik the Red (was he red?), who was in exile and wanted to attract people to a new colony. He thought you should give a land a good name so people would want to go there! It likely was a bit warmer when he landed for the first time than it was when the last settlers starved due to a number of factors — climate change, or at least some bad weather, a major one.
But it was never lush, and their existence was always harsh and meager, especially due to the Viking’s disdain for other peoples and ways of living. They attempted to live a European lifestyle in an arctic climate, side by side with Inuit who easily outlasted them. They starved surrounded by oceans and yet never ate fish! (Note: this was not a typical European behavior, and is a bit of a mystery to this day.)
Instead of hunting whales in kayaks, they farmed cattle, goats, and sheep — despite having to keep them in a barn 24 hours a day, 7 days a week, for a full 5 months out of the year. It was a constant challenge to get enough fodder for the winter. Starvation of the animals was frequent, emaciation routine. Grazing requirements and growing fodder for the winter led to over-production of pastures, erosion, and the need to go further and further afield to sustain the animals. Deforestation for pastures and firewood proceeded at unsustainable rates. After a couple of centuries, it led to such desperate measures as cutting precious sod for housing construction and even burning it for cooking and heating fuel.
When finally confronted with several severe winters in a row, they, along with the little remaining livestock, simply starved before spring arrived.
The moral of the story for the climate controversy? Much as you can not judge a book by its cover, you can’t judge the climate of Greenland by its name.
A bit of related trivia, and further indication of the Vikings’ stubborn reluctance to learn from the Inuit: there is no evidence of any trade whatsoever, despite centuries of cohabitation. In fact, the first of only three Norse accounts of encounters with the natives refers to them as “skraelings” (wretches), and describes matter of factly how strangely they bleed when stabbed. How’s that for diplomacy?
See also the entry on Vineland if it happens to come up.
Sea level in the Arctic is falling
Objection: According to the latest state-of-the-art satellite measurements from over the Arctic, sea levels are falling! Guess all that ice isn’t melting after all.
Answer: Yes, a new study using Europe’s Space Agency’s ERS-2 satellite has determined that over the last 10 years, sea level in the Arctic Ocean has been falling at an average rate of about 2 mm/year. This is very new and very interesting news, though it is preliminary and not published in any peer-reviewed journals yet. But even if these results hold up to time and scrutiny, it is not evidence that globally sea levels are not rising, because they are.
Sea level and sea level change is not uniform around the globe.
Local sea levels are subject to many influences including: wind and ocean currents that can “pile up” the ocean water locally, temperature anomalies like El Niño, local gravity wells of ice sheets and land masses, and regional salinity levels that alter the water’s density. Measurement of these levels is further complicated by changes in land height as the Earth’s crust moves up or down from tectonic motion and rebounds after long and recently ended glaciation, although these complications are avoided by using satellite measurements.
So in short, this is undoubtedly of interest to specialists in several fields, but it does not in any way alter the Global Climate Change picture.
Real Climate has a more detailed writeup on this here.