Is it our fault the Arctic is disappearing?

Hello!! I'm back from my fieldclass in Berlin and so I'll be doing more blog updates from now on. Remember the last time I said I'll be discussing the Arctic ice cover? Well, I shall do so now before moving on to another interesting film. While scientists and researchers do not have conclusive data on whether polar bear numbers are increasing or decreasing, from what I've read so far, it is clear that arctic ice size is indeed shrinking. Annual arctic ice extent has changed by -3% per decade from the late 1970s to the late 1990s, with much more pronounced losses in summer and early autumn (Stroeve et al. 2005, Bjørgo et al. 1997, Cavalieri et al. 1997, Kerr 1999). Recent estimates by the Defense Meteorological Satellite Program Special Sensor Microwave Imager (1987 to present) believe that ice extent has declined by –8.6 ± 2.9% per decade (Serreze et al. 2007). Here is a table that shows the changes in ice sheet in the late 1900s.

This supports the claim that ice sheets in the arctic have truly been decreasing, and so I believe that there should be no debate about that.

What then is the real debate about? The real question that have plagued scientists for a long time is what the definite cause of arctic ice decrease is. Is it natural like Surface Air Temperatures, normal long term climatic warming or human induced warming? When is the arctic ice completely going to disappear if it will at all?

Firstly to answer Al Gore's claim that in 50 - 70 years, the arctic ice will be completely gone, so that's probably in the year 2056 - 2076. In an article by Serreze, the IPCC AR4 models driven with the Special Report on Emissions Scenarios (SRES) A1B emissions scenario (CO2 emissions reaches 720 parts per million by 2100), complete loss of sea ice could occur in from 2040 well beyond 2100. That is a really long time frame. But most models suggest that there would still be a 15% ice cover average output for March and September from 2075 - 2084. Compiling data from 11 models, Serreze presents the projections for March and September in the diagrams below:

The data is still not absolutely conclusive, but from the above data, we agree with Al Gore that ice caps may completely disappear, but not in the time frame that he had dictated (though he did qualify that he got his data from "two major studies")

The next question we need to answer is whether this is a natural phenomenon or a human induced one.

Past ice sheet melting
It must be recognised that this is not the first time that the ice sheet is melting. It has happened before, and it is very spatially dependent. During the early holocene period, insolation was 10% higher than it was in 2004 driven by earth's orbital variations, which led to the deduction of snow and ice cover. This triggered a feedback loop in which a reduction in sea ice would lead to an amplification of warming at high latitudes because (and this we agree with Al Gore), a reduction of sea ice means a reduction in albedo and a higher heat capacity at the Arctic. Hence, more heat can be stored in the summer and re-radiated in winter, creating a positive feedback loop that warms temperatures there. However, the spatial distribution of the warming is not uniform, and some place in the Western Arctic warmed faster than the others. There is a really cool diagram to reflect this:

This diagram shows the holocene thermal maximum that can be studied to try and understand the variation in arctic response to insolation that is observed now, and to try and recognise anthropological and natural reasons for the diminishing arctic ice caps (Kaufman et al. 2004) No where in Al Gore's account of the arctic ice melting did he mention natural factors that lead to the decrease in arctic ice sheets, and he mostly assumes that it was a homogeneous phenomenon, whereas this study has shown us that it is far from that.

Natural factors for arctic ice depletion
There are a few factors that affect ice depletion that are difficult to understand for me. But I shall attempt to explain some of them here.

One of the factors is Arctic Oscillation which is an atmospheric fluctuation that alternately raises and lowers atmospheric pressure over the Arctic while lowering and raising it in a ring around the edge of the polar region. This phenomenon changes wind patterns that affect ice thickness. For example, in a positive phase in 1989, the AO pumped warm air into the arctic and warmed water entering the arctic from the North Atlantic, hence blowing more ice out of the arctic that thinned the ice (Kerr 1999). This in turn leads to a second factor, that of Surface Air Temperature (SAT). Data on SAT usually comes from Russian North Pole measurements collected from drifting buoys and they have calculated a significant increase in temperature from 1920 - 1940, before a cooling period, and then a rise again now. This could be indication that the rise in temperature is due to the AO that affected SAT that had caused warming in the area. Thinner ice caused by warmer SAT as a result of AO is of course much easier to melt, and promotes larger heat fluxes that lead to increased spring SATs, depressing the freezing point and creating earlier spring melts (Stroeve et al. 2004). So here we have a very logical explanation about how humans may not be entirely responsible for the ice melt that is occurring at the Arctic. And it would have been nice if Al Gore had explained that to his audience as well when he discussed Arctic ice melt. One of the authors of one of the articles I read (I can't remember which one really) even suggested that it would take a while before the natural and anthropological causes can be easily separated and identified, though I would suggest that by that time (if we realise conclusively that it is INDEED our fault), it would be too late to reverse the melting.

Anthropological reasons
By stating that there are natural reasons for the ice sheet melt, I do not suggest that humans are free from blame. Most research would suggest that indeed, humans do play a role in ice sheet melting, it just depends on the extent to which they believe so.

An article by Kaufman et al. (2009) suggests that there is in fact a reversal in long term arctic cooling trend that have occurred from 1 C.E. to 1900 C.E. He says that "Assuming that the overall cooling since the HTM was ultimately caused by a decrease in summer insolation, it seems that this insolation anomaly of +1.4% relative to present was amplified by climatic feedbacks". His temperature data is as shown below:

Stroeve (2005) suggests that indeed ice cover may be decreasing from natural factors, but that "external forces may favour a generally more positive AO state. Cooling of the stratosphere, in response to GHG loading or losses in stratospheric ozone can lead to "spin up" of the Polar vortex, favouring a positive shift of the AO" (page 4). This helps us understand the link that Al Gore made between GHG and polar ice melting. We should understand that alone, GHG should not be the sole explanation of melting, rather it speeds up already natural processes or exaggerates the effects to create such phenomenon.

In Conclusion, what we can understand from here is that we need to have a holistic view of the reasons for ice melt. There are historical events of ice melt in the past, and we should only start with our doomsday prophecies if it is certain that this is not just another natural phenomenon that is happening. of course, I am inclined to believe that is is mostly anthropogenic, and greenhouse gases are certainly messing up our natural atmospheric processes, but not everyone may agree with this, so it really depends on which data you would like to take more seriously.

If you want to find out more about the arctic, you can go to my coursemate's blog, which has really indepth research into icesheets in the Arctic. You can go to his blog here:
66 Degrees North


References:
Kaufman D.S. et al. (2004) "Holocene thermal maximum in the western Arctic (0-180degree W)", Quaternary Science Reviews, 23, 529 - 600

Kaufman D.S. et al. (2009) "Recent Warming Reverses Long-Term Arctic Cooling", Science, 325, 1236 - 1239

Stroeve, J.C. et al. (2005) "Tracking the Arctic’s shrinking ice cover: Another extreme September minimum in 2004", Geophysical Research Letters, 32

Serreze, M.C. et al. (2007) "Perspectives on the Arctic's Shrinking Sea-Ice Cover", Science, 315, 1533 - 1536

Kerr, R.A. (1999) "Will the Arctic Ocean Lose All its Ice?", Science, 286, 5446, 1828

Scientific Correspondence "The Arctic's Shrinking Sea Ice", Nature, 376, 126 - 127

Edit: ZOMG found this really funny cartoon... or not so funny. ok nvm.