�鶹��ý

It’s almost unthinkable: the Arctic Ocean, blue all over in summer, with none of the 8 million square kilometres of sea ice — a thin frozen white crust on the ocean surface — that covered it in summer just 40 years ago.

No wonder it made headlines this month when researchers found, as reported by , that “a summer in which the Arctic Ocean features almost entirely open water could be coming even sooner than expected and may become a regular event within most of our lifetimes”.

The research is in observationally-constrained projections of an ice-free Arctic even under a low emission scenario and was published in  on June 6.

It projected “an ice-free Arctic in September under all [emission] scenarios considered”, including low greenhouse gas emission scenarios. In other words, even if emissions are sharply reduced, the Arctic will be ice-free at the end of the northern summer, in September, in coming decades.

If emissions decline only slowly, or continue to rise (as looks likely) the first ice-free summer could be in the 2030s, a decade earlier than projections reported by the Intergovernmental Panel on Climate Change.

Arctic sea ice fluxes from a greater extent in the cold, dark winter months, to a smaller extent in the warmer, 24-hours-a-day light of the northern summer.

The annual average extent was relatively stable in the first half of the 20th century, but started to steadily decrease from the 1950s, with a dramatic collapse in 2007 (see chart below from US Global Change Research Program, 2009).

oberservations_of_annual_average_artic_sea_ice_extent_for_1900_to_2008_gray_shading_indicates_less_confidence_in_the_datat_before_1953_source_us_global_change_research_program_2009.png

Observations of annual average Arctic sea ice extent 1900 to 2008. The gray shading indicates less confidence in the data before 1953. Source: US Global Change Research Program 2009

The new research is a shock to many because it is now clearer that the Arctic, and the global climate system it influences, will suffer almost unimaginable change.

One consequence of a sea ice-free Arctic summer is the large amount of additional heat in the region, as reflective ice is replaced by the heat-absorbing, dark ocean surface.

Greenland is already passed a tipping point for accelerating ice-mass loss, but that will speed up in sea-ice-free conditions.

That means not only a faster rate of sea level rise, but an increasing flow of fresh cold water into the north Atlantic, which will further slow the Atlantic Meridional Overturning Circulation (AMOC, sometimes colloquially called the Gulf Stream, which transports equatorial ocean heat up the north America coast and to Europe).

Then there is the destabilisation of the jet stream, which has and will increasingly lead to more and more extreme sub-Arctic climate events.

artic_meld_has_pushed_the_jet_stream_into_a_more_meandering_s_shape_pattern_dragging_down_and_stalling_cold_and_wet_ocnditions_over_europe.jpg

Arctic melt has pushed the jet stream into a more meandering, S-shape pattern, dragging down and stalling cold and wet conditions over Europe.

This cascade of system-level climate consequences was outlined in ’s recent report .

In September 2007, there was a calamitous drop in the summer Arctic sea-ice extent, such that one well-respected glaciologist responded at the time, in shock, that the sea-ice appeared to be shrinking “100 years ahead of schedule”.

At the time I was transfixed by the event because the implications changed everything. It was clear that the sea-ice had no hope of existing in summer at 2°C of warming which, at that time, was the climate policy-makers’ target.

The evidence was that its tipping point had already passed, and what would be safe for the Arctic and its ecosystem was warming of less than 0.5°C — a measure which has already been exceeded.

The policy-making paradigm was being turned upside down, but few wanted to notice.

The Arctic need to be cooled, urgently, but who wanted that conversation? The case for cooling is even ���ٴǻ岹��.

This was early in my days of writing about climate, and I decided to put down on paper what was happening, what the very good science journalists at that time were saying and, of course what scientists were, and had previously, said about sea ice and Greenland. 

The result was a short report,  of 16 pages. Within a few days, it had been downloaded 20,000 times. This was totally unexpected. The dramatic Arctic story was capturing peoples’ interest and there was a bigger story to tell. 

That understanding led to a decision to write a longer report on other, under-reported, aspects of unexpected and non-linear climate change; a project which within months morphed into the book , with Philip Sutton.

When the news stories were published last week about the new sea-ice projections, I sat down and re-read for the first time in 15 years. What is remarkable is that the cause of the shock today was well understood a decade and a half ago, if one bothered to find out or listen to scientists.

Take this example: “In December 2006, data was presented to an American Geophysical Union conference suggesting that the Arctic may be free of all summer ice by as early as 2030 and likely by 2040.”

This event has been coming for a long time, and the alarm bells have been ringing loudly since at least 2006–07. We ignore history at our peril.

[Reprinted with permission from David Spratt’s �������Dz�.��