ONE TOWN SQUARE: at the intersection of peak oil, climate change, and land use

A new study finds that the world’s fishing industry is depleting older fishing grounds through unsustainable harvesting practices – and that there’s no place left to look for new ones.

The study, titled The Spatial Expansion and Ecological Footprint of Fisheries (1950 to Present), was conducted by researchers at Vancouver’s University of British Columbia in conjunction with the National Geographic magazine.

The study says that 90 million tons of fish were landed in the late 1980s, up from 19 million in the 1950s. The researchers tracked the expansion of fishing activity, examining both the total number of fish caught and the impact that catching different types of fish has had on the ocean’s productivity. By the late 1990s, the world’s fishing fleets had largely run out of new fishing grounds to exploit.

Co-author Enric Sala says we can’t afford to do nothing.

The sooner we come to grips with it, the sooner we can stop the downward spiral by creating stricter fishing regulations and more marine reserves.

The researchers said that in 1950 most heavy fishing was done in the North Atlantic and the Western Pacific, but by the mid 1990s, a third of the world’s oceans and two-thirds of the continental shelves were exploited. That expansion has left only unproductive fishing areas on the high seas and the ice-covered waters of the Arctic and Antarctic for boats to move into.

Here’s the abstract.

Using estimates of the primary production required (PPR) to support fisheries catches (a measure of the footprint of fishing), we analyzed the geographical expansion of the global marine fisheries from 1950 to 2005. We used multiple threshold levels of PPR as percentage of local primary production to define ‘fisheries exploitation’ and applied them to the global dataset of spatially-explicit marine fisheries catches. This approach enabled us to assign exploitation status across a 0.5° latitude/longitude ocean grid system and trace the change in their status over the 56-year time period. This result highlights the global scale expansion in marine fisheries, from the coastal waters off North Atlantic and West Pacific to the waters in the Southern Hemisphere and into the high seas. The southward expansion of fisheries occurred at a rate of almost one degree latitude per year, with the greatest period of expansion occurring in the 1980s and early 1990s. By the mid 1990s, a third of the world’s ocean, and two-thirds of continental shelves, were exploited at a level where PPR of fisheries exceed 10% of PP, leaving only unproductive waters of high seas, and relatively inaccessible waters in the Arctic and Antarctic as the last remaining ‘frontiers.’ The growth in marine fisheries catches for more than half a century was only made possible through exploitation of new fishing grounds. Their rapidly diminishing number indicates a global limit to growth and highlights the urgent need for a transition to sustainable fishing through reduction of PPR.

Global warming is driving forest fires in northern latitudes to burn more frequently and fiercely. Consequently, boreal forests may now giving off more CO2 than they are absorbing.

So concludes a new study published in Nature Geoscience.

University of Guelph professor Merritt Turetsky, lead author of the study, warns of a dangerous feedback loop.

When most people think of wildfires, they think about trees burning, but most of what fuels a boreal fire is plant litter, moss and organic matter in surface soils. These findings are worrisome because about half the world’s soil carbon is locked in northern permafrost and peatland soils. This is carbon that has accumulated in ecosystems a little bit at a time for thousands of years, but is being released very rapidly through increased burning.

Essentially this could represent a runaway climate change scenario in which warming is leading to larger and more intense fires, releasing more greenhouse gases and resulting in more warming. This cycle can be broken for a number of reasons, but likely not without dramatic changes to the boreal forest as we currently know it.

Northern ecosystems are bearing the brunt of climate change.  Longer snow-free seasons, changes in vegetation, loss of ice and permafrost, and now fire are shifting these systems from a global carbon sink toward a carbon source.

Here’s the abstract:

Climate change has increased the area affected by forest fires each year in boreal North America. Increases in burned area and fire frequency are expected to stimulate boreal carbon losses. However, the impact of wildfires on carbon emissions is also affected by the severity of burning. How climate change influences the severity of biomass burning has proved difficult to assess. Here, we examined the depth of ground-layer combustion in 178 sites dominated by black spruce in Alaska, using data collected from 31 fire events between 1983 and 2005. We show that the depth of burning increased as the fire season progressed when the annual area burned was small. However, deep burning occurred throughout the fire season when the annual area burned was large. Depth of burning increased late in the fire season in upland forests, but not in peatland and permafrost sites. Simulations of wildfire-induced carbon losses from Alaskan black spruce stands over the past 60 years suggest that ground-layer combustion has accelerated regional carbon losses over the past decade, owing to increases in burn area and late-season burning. As a result, soils in these black spruce stands have become a net source of carbon to the atmosphere, with carbon emissions far exceeding decadal uptake.

The Sunday New York Times has an article warning that accelerating sea level rise means we’d better start thinking of abandoning some of our coastal areas – even some large cities.

“We can’t afford to protect everything. We will have to abandon some areas.”

The latest science shows we should be planning for a sea level rise of at least 3 feet over this century.

Scientists long believed that the collapse of the gigantic ice sheets in Greenland and Antarctica would take thousands of years, with sea level possibly rising as little as seven inches in this century, about the same amount as in the 20th century.

But researchers have recently been startled to see big changes unfold in both Greenland and Antarctica.

As a result of recent calculations that take the changes into account, many scientists now say that sea level is likely to rise perhaps three feet by 2100 — an increase that, should it come to pass, would pose a threat to coastal regions the world over.

And the calculations suggest that the rise could conceivably exceed six feet, which would put thousands of square miles of the American coastline under water and would probably displace tens of millions of people in Asia.

The scientists say that a rise of even three feet would inundate low-lying lands in many countries, rendering some areas uninhabitable. It would cause coastal flooding of the sort that now happens once or twice a century to occur every few years. It would cause much faster erosion of beaches, barrier islands and marshes. It would contaminate fresh water supplies with salt.

Joseph Romm at Climate Progress has posted a graph showing sea level rise in three scenarios.  Of course we’re on track for the worse-case scenario which would result from our “do nothing” policies, where the midpoint of the range of sea level rise is nearly five feet.

The Times article says Orrin H. Pilkey of Duke University, one of the deans of American coastal studies, is advising coastal communities to plan for a rise of at least five feet by 2100. Romm points out that Pilkey in fact is advising to plan on a rise of at least seven feet.

Oregon Shores Conservation Coalition recently proposed a new Goal 20, which would require Oregon communities to begin planning for sea level rise. Oregon Shores’ draft goal assumed a modest 2-foot rise by 2100, about half the sea level rise considered likely in the 2009 report  The Impacts of Sea-Level Rise on the California Coast prepared for California’s Interagency Climate Action Team by the Pacific Institute. Oregon Shores’ proposal, inadequate as it was, was dismissed by the Land Conservation and Development Commission.

Especially after the most recent election results, planning for anything other than a continuation of business as usual is a non-starter, in the U.S. as well as here in Oregon. We will continue to do nothing until we are literally swamped by events.

Comparison of 2010 Temperature to the Two Other Years with the Warmest Annual Means

Line plot of global mean land-ocean temperature index, 1880 to present, with the base period 1951-1980. The dotted black line is the annual mean and the solid red line is the five-year mean. The green bars show uncertainty estimates.

On September 15 the National Snow and Ice Data Center reported Arctic ice extent had started increasing again, calling September 10 the end of the 2010 Arctic melt season and pegging 2010 as the third-lowest ever recorded, behind 2007 and 2008.

But not so fast! Their daily image update shows sea ice extent declining again. Sea ice extent has now fallen below that recorded on September 10.

The late-season dip shows up even better in this chart at the Japan Aerospace Exploration Agency website.

The IJIS website explains why their data may differ slightly from NSIDC’s:

In general, sea-ice extent is defined as a temporal average of several days (e.g., five days) in order to eliminate calculation errors due to a lack of data (e.g., for traditional microwave sensors such as SMMR and SSM/I). However, we adopt the average of two days to achieve rapid data release. The wider spatial coverage of AMSR-E enables reducing the data-production period.

Sea ice extent is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean).

NSIDC reported sea ice extent on September 10, 2010 at 4.76 million km². According to IJIS, the minimum as of September 17 was 4.83 million km² – 120,000 km² below the September 10 extent of 4.95 million km² and just 130,000 km² above the minimum extent of 470,7813 km² reached on September 9, 2008.

Note that IJIS data on sea ice extent differs slightly from NSIDC data. The IJIS web site explains that they average the most recent two days of data rather than the more widespread methodology of averaging five days of data to “achieve rapid data release.” But this wouldn’t seem to explain why their numbers are higher than NSIDC’s.

Ice extent has been falling more than 50,000 km² a day for the past four days.  If that decline keeps up for just a couple more days, the 2010 minimum extent would dip below the 2008 mark and become the second lowest ever recorded.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice appears to have reached its annual minimum extent on September 10. This melt season confirms that the trend of decreasing summer sea ice is continuing.

The minimum ice extent was the third lowest in the satellite record, after 2007 and 2008.

This is only the third time in the satellite record that ice extent has fallen below 5 million square kilometers (1.93 million square miles) – and all those occurrences have been within the past four years.

Assuming that we have indeed reached the seasonal minimum extent, 2010 came respectably near record lows despite seeing the shortest melt season in the satellite record. The melt season got a late start and appears to have ended early, spanning only 163 days between the seasonal maximum and minimum ice extents.

Joseph Romm at Climate Progress reports that scientists confirm the oldest, thickest ice is disappearing.

NSIDC scientist Julienne Stroeve explains what this chart means:

This figure would support thinning of the icepack over the last couple of decades since older ice tends to be thicker than younger ice. You can see in this figure how little of the really old, and thick ice there is left in the Arctic Basin.

The Polar Science Center, using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), calculates that the monthly average Arctic Sea Ice Volume for May 2010 was the lowest May volume over the 1979–2010 period, 42% below the 1979 maximum and 32% below the 1979–2009 May average. So far, September 2009 holds the record for lowest ice volume, at 67% below its 1979 maximum. We’ll soon see if that record will be broken in 2010.

The combined global land and ocean surface temperature for January–August 2010 tied with 1998 as the warmest such period on record, according to NOAA National Climatic Data Center’s newly released  State of the Climate Global Analysis August 2010.

The Northern Hemisphere as a whole experienced its warmest August on record, surpassing the previous record set in 2003. Separately, the Northern Hemisphere land surface temperature was the warmest on record. Only relatively cool temperatures in the Southern Hemisphere (11th warmest on record) held global August temperatures at the third highest on record, behind 1998 and 2009.

As this chart shows, the world has been steadily growing warmer since the industrial revolution kicked in near the end of the 19th century.

The consequences of more than a century of the profligate burning of fossil fuels are becoming manifest:

• The August worldwide land surface temperature was the second warmest August on record, behind 1998.
• The June–August worldwide land surface temperature was the warmest June–August on record, surpassing the previous June–August record set in 1998.
• In the Northern Hemisphere, it was a hot, hot summer. The June-August period was the warmest on record, surpassing 1998 and 2005.

The National Snow and Ice Data Center (NSIDC) confirms that the Northwest Passage and the Northern Sea Route are largely free of ice, allowing the potential for a circumnavigation of the Arctic Ocean.

The minimum ice extent for the year will probably occur in the next two weeks.

At the end of August, ice extent had fallen to the fourth lowest in the satellite record, behind the seasonal minima recorded for 2007, 2008, and 2009. On September 3, ice extent fell below the seasonal minimum for 2009 to claim third lowest on record.

At Climate Progress, Joseph Romm reports that a major analysis, titled “History of sea ice in the Arctic”, finds that there is less ice covering the Arctic today than at any time in recent geologic history.

This is from the abstract:

[E]pisodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorter-term (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.

In the past, the Arctic thawed because of changes in Earth’s orbit. This time, it’s due to human emissions.

Romm quotes lead author Leonid Polyak’s response to the question, when was the last time the Arctic was ice free?

The paleo data we have so far is very scant, so we can’t know for sure when the Arctic was ice free in the summer last time. To be conservative, the closest candidate is the early Holocene (roughly ~10 kyr ago), when the insolation in the Arctic was high due to the beneficial orbital configuration; however, the more data I see, the stronger is my impression that there was not that little ice at that time. The next best (actually, better) candidate is the Last Interglacial, about 125kyr ago, again due to orbitally-driven high insolation: the ice was likely very low, but we can’t say whether it was completely ice free in summer or not. There are also a few other major interglacials, which may have had a similar picture, in particular Marine Isotopic Stage 11, about 450 kyr ago. In any case we are talking about very rare events controlled by a forcing very different from today. If none of those intervals was really ice free, then a million year assessment would be correct.

External forcings – primarily orbital in the past and primarily greenhouse gases now – are further boosted by Arctic amplification, primarily positive feedbacks from the retreat of ice and snow. The Arctic warming threatens to set off a cascade of effects, including speeding up the melting of the Greenland ice sheet, accelerating the rise in sea levels; and even more serious, melting of the permafrost. Release of even a fraction of the methane stored in the permafrost (the East Siberian Arctic Shelf, for example) could trigger abrupt and catastrophic climate warming.

The evidence is undeniable: human-caused greenhouse gas emissions are overwhelming the system.

A study published in the September issue of the Journal of the Geological Society found that increasing CO2 levels are causing foram diversity to plummet:

A unique ‘natural laboratory’ in the Mediterranean Sea is revealing the effects of rising carbon dioxide levels on life in the oceans. The results show a bleak future for marine life as ocean acidity rises, and suggest that similar lowering of ocean pH levels may have been responsible for massive extinctions in the past.

Rising carbon dioxide levels acidify the ocean, which has a particularly devastating effect on organisms that have calcium carbonate shells, like Foraminifera. The study, published in the September issue of the Journal of the Geological Society, found that increasing CO2 levels caused foram diversity to fall from 24 species to only 4. The study found a tipping point occurs at mean pH 7.8, the pH level predicted for the end of this century.

Forams record past events in the geological record. The Paleocene-Eocene Thermal Maximum (PETM), 55 million years ago, was a period of massive carbon release and rapid warming, accompanied by extinctions in marine life.

This statement by study co-author Dr. Jason Hall-Spencer in the Geological Society’s press release is not optimistic:

Our natural laboratory provides a glimpse into the future of our oceans.

Joseph Romm at Climate Progress has posted this chart showing trends in ocean CO2 concentrations and pH at one sampling station off Hawaii.

Romm also points out that the disappearance of forams has grave implications for the rest of the food chain.

For an analysis of what that could mean, see 2009 Nature Geoscience study concludes ocean dead zones “devoid of fish and seafood” are poised to expand and “remain for thousands of years.”

A study published in the journal Global Change Biology reports the discovery of very similar colonies of bryozoans – animals that anchor themselves to the seabed – in both the Ross and Weddell Seas.

The bryozoans, sometimes called moss animals, are often microscopic as individuals but form colonies that can look like corals or some seaweeds. Those found were unlike others around the current coast of Antarctica.

So,what’s the big deal?

Bryozoans are largely static and their larvae, dispersed by currents, are short-lived and quickly sink. How is it possible that two virtually identical populations came to exist 2400 kilometers apart, separated by the 2 kilometre thick West Antarctic ice sheet?

An article at ABC News in Science quotes lead author David Barnes:

The most likely explanation of such similarity is that this ice sheet is much less stable than previously thought and has collapsed at some point in the recent past. And if the West Antarctic ice shelf has been lost in recent times we have to re-think the possibility of loss in future with climate change.

If the ice were gone a passage would become open through which currents could carry the larvae between the two seas.

Melting of the West Antarctica ice cap would raise world sea levels by between 3.5 and 5 meters. In a brief warm period about 125,000 years ago, world sea levels were about five meters higher than today and temperatures probably at least 4°C warmer.

A good friend recently asked me why I give so much attention to news about Arctic sea ice extent at this blog, saying he just glosses over posts on this subject.

Here’s the reason: the area of sea ice cover is an important, amplifying climate feedback. Loss of sea ice is a cause of concern because as the area of ice decreases, increased absorption of sunlight by the darker ocean causes more sea ice melting. As this graph from Makiko Sato & James Hansen’s new blog shows, Arctic sea ice extent has been declining steadily . . .

. . . as has sea ice volume. What ice remains is getting thinner.

It’s not just sea ice that is melting. Ice sheets are shrinking too, both in Greenland and in Antarctica.

And the ice loss over the last few years has been at a time of minimum solar irradiance. Solar irradiance is now once again on the upswing.

It seems likely that September Arctic sea ice may be all but gone within a few decades – or perhaps even sooner. What does less Arctic sea ice mean for Earth’s weather patterns?

NASA is predicting loss of summer sea ice will mean more severe winter storms in the northern hemisphere – a prediction which is already being borne out.

Following Arctic sea ice extent is fascinating because it shows that global warming is not something to worry about in the future. Global warming is here and now, and is already affecting us in our daily lives. What’s worrisome is that the impacts will only get more severe. By the time the impacts are bad enough to get our attention, it will be too late – the damage will already have been done. Under the best-case scenario it will take Earth a thousand years or more to recover. Under the worst-case scenario, Earth will flip into a different, stable climate regime which won’t be hospitable to human existence.

Above: cumulative annual area changes for 34 of the widest Greenland ice sheet marine-terminating outlets. Source: Byrd Polar Research Center.

Location of the successive calving fronts of the Jakobshavn Isbrae glacier between 1851 and 2009, overlain on a Landsat image from 7/29/2009. Source: NASA/Goddard Space Flight Center Scientific Visualization Studio. Historic calving front locations courtesy of Anker Weidick and Ole Bennike, Geological Survey of Denmark and Greenland.

Microscopic life crucial to the marine food chain is dying out. The consequences could be catastrophic.

So reads the headline of an article in the U.K. Independent reporting on new research published in the journal Nature. The study, titled Global phytoplankton decline over the past century, finds there has been a 40% decline in the ocean’s phytoplankton over the last 100 years – and global warming is to blame.

The microscopic plants that support all life in the oceans are dying off at a rate of about 1% per year. The decline is related to rising sea surface temperatures.

According to the Independent, the scientists said if the findings are confirmed by further studies, the decline in phytoplankton will represent the single biggest change to the global biosphere in modern times, even bigger than the destruction of the tropical rainforests and coral reefs. Phytoplankton are microscopic marine organisms capable of photosynthesis, just like terrestrial plants. They float in the upper layers of the oceans, provide much of the oxygen we breathe and account for about half of the total organic matter on Earth. Phytoplankton are the basis of life in the oceans and are essential in maintaining the health of the oceans. A 40% decline would represent a massive change to the global biosphere.

The press release explains that in warmer oceans, the water becomes stratified, with warmer water on top of colder deeper water. Nutrients which are normally replenished by upwelling colder water are cut off, and the photosynthesizers living in the surface waters starve to death.

Rising sea surface temperatures were negatively correlated with phytoplankton growth over most of the globe, especially close to the equator. Phytoplankton need both sunlight and nutrients to grow; warm oceans are strongly stratified, which limits the amount of nutrients that are delivered from deeper waters to the surface ocean. Rising temperatures may contribute to making the tropical oceans even more stratified, leading to increasing nutrient limitation and phytoplankton declines.

Dave Cohen points out we’re caught in a nasty downward spiral:

It is clear that we have a disastrous positive feedback loop at work here, in which warmer surface water supports fewer phytoplankton, which then take up less CO₂ from the atmosphere, which causes the surface water to warm some more due to the greenhouse effect, etc.

Here’s the abstract of the Nature article:

In the oceans, ubiquitous microscopic phototrophs (phytoplankton) account for approximately half the production of organic matter on Earth. Analyses of satellite-derived phytoplankton concentration (available since 1979) have suggested decadal-scale fluctuations linked to climate forcing, but the length of this record is insufficient to resolve longer-term trends. Here we combine available ocean transparency measurements and in situ chlorophyll observations to estimate the time dependence of phytoplankton biomass at local, regional and global scales since 1899. We observe declines in eight out of ten ocean regions, and estimate a global rate of decline of ~1% of the global median per year. Our analyses further reveal interannual to decadal phytoplankton fluctuations superimposed on long-term trends. These fluctuations are strongly correlated with basin-scale climate indices, whereas long-term declining trends are related to increasing sea surface temperatures. We conclude that global phytoplankton concentration has declined over the past century; this decline will need to be considered in future studies of marine ecosystems, geochemical cycling, ocean circulation and fisheries.

The National Oceanic and Atmospheric Administration (NOAA) has released the 2009 State of the Climate report, which concludes the scientific evidence that our world is warming is unmistakable. The past decade was the warmest on record and that the Earth has been growing warmer over the last 50 years.

Human society has developed for thousands of years under one climatic state, and now a new set of climatic conditions are taking shape. These conditions are consistently warmer, and some areas are likely to see more extreme events like severe drought, torrential rain and violent storms.

Deke Arndt, co-editor of the report and chief of the Climate Monitoring Branch of NOAA’s National Climatic Data Center, is quoted in NOAA’s press release:

The temperature increase of one degree Fahrenheit over the past 50 years may seem small, but it has already altered our planet. Glaciers and sea ice are melting, heavy rainfall is intensifying and heat waves are more common. And, as the new report tells us, there is now evidence that over 90 percent of warming over the past 50 years has gone into our ocean.

Regarding warming oceans, the report says warming has been observed as far as 6,000 feet below the surface, but most of the heat is accumulating in the oceans’ near-surface layers. The implications of a warming ocean are considerable. First, because water expands as it warms, ocean heating is responsible for much of the observed sea-level rise (melting of land-based ice is responsible for the rest). Further, the oceans will hold the heat they’ve accumulated because they warm and cool much more slowly than air – meaning the impacts of warming will continue to be felt long after greenhouse gas emissions peak and begin to decline, should humans ever manage to muster the wisdom and the will to make that happen.

The National Oceanic and Atmospheric Administration reports the global combined land and ocean surface temperature average for May was the warmest on record. The globally averaged temperature for both land and ocean surfaces was 0.69°C (1.24°F) above the 20^th century average of 14.8°C (58.6°F).

May 2010 Blended Land and Sea Surface Temperature Anomalies in degrees Celsius

The combined global land and ocean surface temperature during March–May 2010 was 14.4°C (58.0°F) and ranked as the warmest such period on record, 0.73°C (1.31°F) above the 20^th century average of 13.7°C (56.7°F).

March 2010 – May 2010 Blended Land and Sea Surface Temperature Anomalies in degrees Celsius

The warmest anomalies occurred over eastern and northern North America, eastern Brazil, northern Africa, eastern Europe, and southern Asia. See the deep red dots along the land masses of the Arctic and in southern Greenland and the eastern U.S. and Canada. Anomalously cool conditions were present over eastern Asia and the western United States.

Looks to be a long, hot summer.

May Global Hemisphere plot

The National Snow and Ice Data Center (NSIDC) reports that by the end of May, Arctic ice extent had fallen to near the 2006 level, the lowest in the satellite record for the end of that month.

NSIDC explains why Arctic ice went so rapidly from near normal to approach record lows:

[S]everal regions of the Arctic experienced a late-season spurt in ice growth. As a result, ice extent reached its seasonal maximum much later than average, and in turn the melt season began almost a month later than average. As ice began to decline in April, the rate was close to the average for that time of year. In sharp contrast, ice extent declined rapidly during the month of May. Much of the ice loss occurred in the Bering Sea and the Sea of Okhotsk, indicating that the ice in these areas was thin and susceptible to melt. Many polynyas, areas of open water in the ice pack, opened up in the regions north of Alaska, in the Canadian Arctic Islands, and in the Kara and Barents and Laptev seas.

The polynyas are clearly visible in high-resolution passive microwave images from the Advanced Microwave Sounding Radiometer (AMSR-E) aboard NASA’s Aqua satellite. What do current ice conditions mean for the minimum ice extent this fall? It is still too soon to say: although ice extent at present is relatively low, the amount of ice that survives the summer melt season will be largely determined by the wind and weather conditions over the next few months.

Analysis from scientists at the University of Washington shows that ice volume has continued to decline precipitously.

Joseph Romm comments at Climate Progress on a presentation by Wieslaw Maslowski of the Naval Postgraduate School, one of the country’s leading experts on the Arctic, indicating the Arctic is in a death spiral.  By 2016 (+/- 3 yrs) the Arctic will be essentially ice-free by the end of the melt season – decades ahead of the projections in the 2007 IPCC report.

And here’s the latest multi-year chart of Arctic ice extent from the Japan Aerospace Exploration Agency website.

The National Snow and Ice Data Center reports that, after a late start, Arctic sea ice extent has now dipped below 2007 levels at this stage of the melt season. 2007 is the year Arctic sea ice reached its record low extent.

The Japan Aerospace Exploration Agency (JAXA) has a terrific graphic on its website showing multiple years of Arctic ice extent. As you can see, it’s much too early to predict that 2010 will see a new record low, although conditions in the Arctic such as areas of open water in the pack ice and broad areas of more scattered ice cover indicate that the ice may be posed to retreat rapidly.

The area of sea-ice cover is often defined in two ways: sea-ice “extent” and sea-ice “area.” Sea ice extent is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean), whereas the “area” definition counts only sea ice covering a fraction of the ocean (sea ice only). Thus, the sea-ice extent is always larger than the sea-ice area.

Regardless of ice extent, Arctic ice volume continues to hit record lows.

A new paper in the journal Nature titled Robust warming of the global upper ocean concludes that the world’s oceans have been warming more than previously thought – and more than even climate models were suggesting.

RealClimate has posted this graph showing the measured warming as compared to previous and model estimates:

Basically, if the total flux of energy entering the Earth’s atmosphere is greater than energy losses, then has to go somewhere – and that somewhere is mainly the ocean. Other reservoirs for this excess energy, like the land surface or melting ice, are much smaller and are for most purposes negligible.

An article about the study by Jason Socrates Bardi quotes Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado (Trenberth was not involved with the study):

Ninety percent of the energy [trapped by increased greenhouse gases] goes into the ocean. It’s important to track this in order to properly understand what is happening in the climate system. If you dump heat in the ocean and it gets moved around and reappears somewhere, it has consequences in terms of the weather patterns.

Another new study in the journal Oceanography titled The Volume of Earth’s Ocean finds the Earth’s ocean is smaller  than the most recent published estimates, by a volume equivalent to 500 times the Great Lakes or five times the Gulf of Mexico. The study’s authors used satellite altimetry data to better measure ocean depth and thus to more accurately estimate the ocean’s volume.