One of the most obvious of these effects is the decline in Arctic Sea Ice.
The graphs is Figure 1 and Figure 2, show that Arctic Sea Ice has been declining ever since satelite measurements became available in 1979. Although there is year to year variation the trends in both maximum sea ice and minimum seaice are negative. Figure 1 shows that 2007 was a particularly bad year for the sea ice with a spectacular drop in sea ice minimum extent. Although 2008 and 2009 minimums were higher than 2007 they are still respectively the second lowest and third lowest levels on record. The "recovery" has just returned levels back to that of the declining trend line.
figure 1. Arctic Sea Ice trend at the end of the melt season since 1979 Source:
figure 2. Arctic Sea Ice trend of maximum sea ice levels since 1979 Source:
The question arises: "What is currently happening to the Arctic Sea Ice?" Figure 3 and Figure 4 show the changes to the sea ice since last year's minimum extent. It is clear from them that the ice grew quite slowly during the northern winter - it started from a higher level than 2007 but followed the 2007 trajectory for most of the ice growing season. For about a month the ice extent was close to the long term average but for the last month and a half has declined very quickly.
As an aside it is interesting to note how the global warming deniers handle this information. The denier's approach is to ignore the larger picture - for instance you will never see figures 1 and 2 on a denier site - instead they search through a mountain of contrary evidence to find anything that can be manipulated to provide the answer that they desperately desire. It is hardly surprising then that as soon as the ice neared the average values the denier sites started claiming that the ice isn't declining as it is near average levels. It is irrelevant to such people that the ice approached average levels for a short period of time. Here is a post by Australia's premier denier during that short period of time.
The sea ice decline has been dramatic since the beginning of May. The amount of ice lost in May 2010 is the largest amount lost in any May in the record. As the NSIDC noted in the June 8 2010 update:
Arctic sea ice extent averaged 13.10 million square kilometers (5.06 million square miles) for the month of May, 500,000 square kilometers (193,000 square miles) below the 1979 to 2000 average. The rate of ice extent decline for the month was -68,000 kilometers (-26,000 square miles) per day, almost 50% more than the average rate of -46,000 kilometers (18,000 square miles) per day. This rate of loss is the highest for the month of May during the satellite record.
Figure 5 shows that currently the Arctic Sea Ice extent is at its lowest recorded level for this time of year.
figure 3. Arctic Sea Ice Levels - March to Jume 2010 Source: NSIDC
figure 4. Arctic Sea Ice levels September 2009 to January 2010, Source: NSIDC
figure 5. Arctic Sea Ice levels since 2003, source: AMSR-E
Ice extent is not the only method of measuring Arctic Sea Ice, an alternative is to determine ice volume. The Polar Science Center (PSC) has developed a method of determining Arctic Sea Ice Volume. The PSC arctic ice volume chart can be seen in Figure 6. Note that, like the ice extent data, this also has a long term downward trend. As well the apparent "recovery" since 2007 does not appear in volume information. In fact, ice volume has declined since 2007 and currently is at its lowest level.
Deniers will immediately cry foul, as this chart is produced by a combination of observation and modelling. The results, though, have been carefully validated in relation to the ICEsat satelite. ICEsat measurements, which have in turn been validated by measurements taken by US Navy submarines, have confirmed that Arctic sea ice volume is significantly declining.
Here are some quotations from the ICEsat site:
The Arctic ice cap grows each winter as the sun sets for several months and intense cold ensues. In the summer, wind and ocean currents cause some of the ice naturally to flow out of the Arctic, while much of it melts in place. But not all of the Arctic ice melts each summer; the thicker, older ice is more likely to survive. Seasonal sea ice usually reaches about 2 meters (6 feet) in thickness, while multi-year ice averages 3 meters (9 feet).
Using ICESat measurements, scientists found that overall Arctic sea ice thinned about 0.17 meters (7 inches) a year, for a total of 0.68 meters (2.2 feet) over four winters. The total area covered by the thicker, older "multi-year" ice that has survived one or more summers shrank by 42 percent.
In recent years, the amount of ice replaced in the winter has not been sufficient to offset summer ice losses. The result is more open water in summer, which then absorbs more heat, warming the ocean and further melting the ice. Between 2004 and 2008, multi-year ice cover shrank 1.54 million square kilometers (595,000 square miles) -- nearly the size of Alaska's land area.
During the study period, the relative contributions of the two ice types to the total volume of the Arctic's ice cover were reversed. In 2003, 62 percent of the Arctic's total ice volume was stored in multi-year ice, with 38 percent stored in first-year seasonal ice. By 2008, 68 percent of the total ice volume was first-year ice, with 32 percent multi-year ice
Figure 6. Arctic Sea Ice Volume. Source PSC
Evidence for the decline in Arctic sea ice thickness has been found by polar scientists visiting the Arctic. Figure 7 is a video of a relatively brief talk given by Dr David Barber. The implications of his eye witness account are quite sobering. A longer and more detailed talk on this topic can be found here.
Figure 7. Direct observations of sea ice by scientists
So, what is my prediction for sea ice minimum in 2010? I expect that this year's ice minumum will be between the 2007 level and the 2009 level. The sea ice minimum in 2007 was exceptional, and I expect that this year's ice melt will not reach the same low level. The ice is very thin, though, and susceptible to melt, so it could quite well be lower than last year.
We will know in September.
Peter Sinclair has produced a video on the topic of Arctic Sea Ice. It covers many of the points made in this post, but is still well worth watching, as Sinclair has an interesting and direct style.
In the post I made the (not very brave) prediction that this year's melt would be between that of 2007 and 2010. That turned out to be true. As NSIDC noted:
Ice extent for September 2010 was the third lowest in the satellite record for the month, behind 2007 (lowest) and 2008 (second lowest).
Here is the NSIDC graph:
Here is the AMSR-E graph:
The main issue though is the long term trend. As NSIDC notes:
The linear rate of decline of September ice extent over the period 1979 to 2010 is now 81,400 square kilometers (31,400 square miles) per year, or 11.5% per decade relative to the 1979 to 2000 average.
Here is the NSIDC trend graph:
It might be that a linear trend is not the best way of showing the trend. Tamino has fitted a quadratic trend line to the data, and it looks like a very good fit. This indicates that the declining trend might be accelerating. Here is Tamino's graph:
The cross at the right is the actual lowest level for this year.
Climate disinformers keep missing the point and keep making fools of themselves.
Here is a video by Peter Sinclair on the effects of warming on planetary ice which incudes absurd claims by climate disinformers which are contradicted by a scientist and an admiral in the US navy: