A sea-ice free Arctic by 2028, and other chilling facts

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The latest and best climate science is not recommended for bedtime reading. The globe is already committed to warming in excess of dangerous levels

This Climate Change Science Compendium is a wake-up call. The time for hesitation is over. We need the world to realize, once and for all, that the time to act is now--Ban Ki Moon (Secretary General of the United Nations, September 2009)

Publication of the Climate Change Science Compendium 2009 (United Nations Environment Programme, September 2009) coincided with the pre-Copenhagen global leaders’ summit in New York. It updates scientists’ evolving understanding of earth system science, to inform climate change policy-making.

The picture painted by the compendium of the immediacy and scale of global warming makes The Inconvenient Truth look like a Disney movie. Its message is the need to avoid the unmanageable, whilst managing the unavoidable. Quite a lot of damage, it says, is already unavoidable.

On subjects where the science is disputed or equivocal, this publication treads warily, or says nothing at all. Conversely, where observations or predictions are ventured, they can be regarded as authoritative. A brief summary follows: one would rather know, than not, what’s going to happen, and when, and what else is at stake.

It’s happening now
You might, like me, have watched the news lately – drought-related conflict in Kenya, the typhoon-deluged Philippines, last summer’s bushfires in Victoria, the dust storm over Sydney, metre-deep snow on our own Napier-Taupo road in October, commercial shipping traversing the North West passage – and wondered what, if anything, it signifies.

The compendium starts by depicting “significant climate anomalies” from 2008 and 2009. It shows extreme weather events on every continent, and extremes within each continent. Here are a few of them:

  • The largest Northern Hemisphere January snow cover on record; and record lows of September Arctic sea ice in both 2007 and 2009, surpassing the previous record set in 2005 by 23 percent.
  • In Mexico, the worst drought in 70 years; and the same year in Brazil, the worst deluge in more than 20 years.
  • Hurricane Bertha, the longest-lived July Atlantic tropical storm on record (17 days).
  • In the United Kingdom, one of 10 wettest summers on record, and 190 kilometre/hour winds in France and Spain.
  • The worst floods in a century for Algeria; and in Kenya, the worst drought in almost two decades.
  • In the Middle East, the heaviest snowfall in more than a decade in Iran, and the first snowfall in living memory in Baghdad.
  • In China, the severest winter weather and the worst drought in 50 years.
  • The warmest August for both Australia and New Zealand since records began, respectively, 60 and 155 years ago.

Scientists believe that our greenhouse gas emissions to date have already committed the world to average warming of 2.4 degrees celsius – surpassing the two degrees previously identified as a dangerous risk. Thus far, 0.6 of a degree of that warming has been realised. The remainder will develop in the years to 2100.

Looking at what the world is experiencing already, the effects will be more than trifling.

Still heading in the wrong direction
The IPCC’s worst-case emissions scenarios have been exceeded. Man-made emissions have risen 38 percent above 1990 levels. They rose on average 3.5 percent per year for the period 2000-2007, an almost four-fold increase on the previous decade’s average of 0.9 percent per year. The compendium reminds us that, to date, “no region is decarbonising its energy supply”.

Glacier and ice cap volumes
Near universal retreat and volume loss of glaciers and ice caps threaten the well-being of around one-sixth of the world’s population and co-located ecosystems, whose water depends on glacier ice and seasonal snow. If they melted completely, they would contribute to sea level rise (up to 0.7 metres).

The previous record loss in 1998 of 30 monitored glaciers in nine mountain ranges has been exceeded three times this century, and the new record loss in 2006 was almost double that of 1998. The current total extent and volume of glaciers and ice caps is now approaching or exceeding the lowest value in about 10,000 years. If current trends continue, some mountain ranges including the Pyrenees and the mountains of tropical Africa will be ice free in the next few decades.

Arctic sea ice
The extent of Arctic sea ice is declining; there is a “very low probability that it will ever recover”. The Arctic could be ice free in summer within 20 years, not the waning years of this century as had previously been thought. NASA satellite images show a decline in total winter sea ice volume, and a diminishing proportion of multi-year ice compared to first year ice. First year ice melts more quickly.

That exposes more water to the sun earlier in the year, increasing sea and air temperatures, and affecting ice formation, ice melting, and the melting of permafrost. It is not known how much greenhouse gas is currently sequestered in frozen Arctic soils; one recent report put it at twice current atmospheric levels. This is why the Arctic matters, and is described as a tipping point.

Ice sheets: Greenland and Antarctica
The Greenland ice sheet, if completely melted, would raise sea level by around eight metres; the compendium signals a potential six metre rise from this source in coming centuries. A large increase in melt was observed in 2007, 60 percent more than the previous high in 1998 – up to 50 more days of melt than average in some locations, up to 30 days earlier than average.

In Antarctica, last year’s collapse of the 1.3 million hectare Wilkins ice shelf serves as a “dire warning”. The ice shelves buttress the ice sheets. If completely melted, Antarctica’s ice sheets would raise sea levels by approximately 57 metres. The compendium doubts whether topography will allow this to occur, although there is ample geological evidence of similar events before; it posits a 3.3 metre sea level rise from this source over the long term, centuries to millenia. Luckily for us, Antarctica is more stable than the Arctic. Learning how the region is responding offers scientists an “exciting challenge”.

Sea level rise
A plausible range for global average sea level rise of 0.5 to 2.0 metres by 2100 is suggested, due to thermal expansion and ice melt – much more than the upper limit of 59 centimetres previously predicted by the IPCC.

Currently, about 100 million people worldwide live within a metre of sea level. The impacts of sea level rise will be felt through both the change in normal levels, and extreme weather events such as storm surges. Modelling shows that a 50 centimetre rise would produce tidal events every day that now occur once a year, and events expected once during the whole of the 20th century will occur several times every year by 2100.

Ocean acidification
The ocean absorbs carbon dioxide, which alters its chemistry. Average surface ocean acidity has been altered to 8.1 pH units from a pre-industrial value of 8.2 on a logarithmic scale – that is, a 30 percent increase in acidity. At current emission rates, an average of 7.9-7.8 pH units is expected.

Ocean acidification affects the habitat of creatures that need calcium carbonate for their shells and bones. The total effects on the marine environment are unclear, but it has been implicated in algae formation. Some scientists think algae would be beneficial, because it absorbs carbon; others dispute the net effect.

Thermohaline circulation
Fresh water inflow changes from ice melt could affect the turnover from ocean surface to deep water, and vice versa, that drives the Gulf Stream, and the ocean’s absorption and release of carbon dioxide. The compendium offers no answers, but some comments on why it really matters: upwelling may have been a major contributor to the increase in atmospheric carbon during Pleistocene deglaciation, and carbon dioxide absorption by the oceans accounts for up to 40 percent of current emissions.

The consequences for New Zealand might seem, by contrast, relatively benign and manageable – but it would not be benign for us to stand by and watch, and run the larger unmanageable risks.