It is the most typical day this decade for the annual Arctic ice extent minimum. Some take any year’s slightly lower minimum as proof that Arctic ice is dying, but the image below shows extents from 2007, mostly smaller than 2017.

While the daily average extent for the last 10 years bottomed out on day 260, years like 2016 and 2009 hit minimum on day 254.  This year’s extent was at 4.7M km2 for a week, hit bottom at 4.6M on day 253, then rose up and over 4.8M km2.  SII (Sea Ice Index) 2017 is similar to MASIE, though a bit lower lately. The graph below shows September comparisons at day 260.
Note that as of day 256, 2017 has gone 300k km2 above average, 500k km2 more than 2016, 700k km2 higher than 2007, and 1400k km2 greater than 2012.  All regions have added ice, with Central Arctic the only exception.  That is likely due to Central Arctic sea already full of ice at 3.1M km2.

The table shows ice extents in the regions for 2017, 10 year averages and 2007 for day 260.

The largest deficits to average are in BCE and Greenland Sea, more than offset by huge surpluses in Central Arctice, CAA and Laptev.

Over this decade, the Arctic ice minimum has not declined, but looks like fluctuations around a plateau since 2007. By mid-September, all the peripheral seas have turned to water, and the residual ice shows up in a few places. The table below indicates where  ice is found in September. (Shows day 260 amounts with 10 year averages)

BCE (Beaufort, Chukchi and East Siberian) on the Asian side are quite variable as the largest source of ice other than the Central Arctic itself.   Greenland Sea and CAA (Canadian Arctic Archipelago) together hold almost 0.5M km2 of ice at minimum, fairly consistently.   LKB are the European seas of Laptev, Kara and Barents, a smaller source of ice, but a difference maker some years, as Laptev was in 2016 and 2017.  Baffin and Hudson Bays are almost inconsequential.  The biggest contributors to 2017 success are Central Arctic, Canadian Archipelago and Laptev.

For context, note that the average maximum has been 15M, so on average the extent shrinks to 30% of the March high before growing back the following winter.

Footnote

Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used. This is false in fact and in logic. Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year? Researchers do this, including Walt Meier in charge of Sea Ice Index. That said, I understand his interest in directing people to use his product rather than one he does not control. As I have said before:

MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies. More on this at my post Support MASIE Arctic Ice Dataset

via Science Matters

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September 18, 2017 at 05:44PM

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September 18, 2017 at 04:33PM

A report published 3 years ago by the Global Warming Policy Foundation showed that the best observational evidence indicates our climate is considerably less sensitive to greenhouse gases than climate models are estimating.

The clues for this and the relevant scientific papers are all referred to in the Fifth Assessment report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). However, this important conclusion was not drawn in the full IPCC report – it is only mentioned as a possibility – and is ignored in the IPCC’s Summary for Policymakers (SPM).

For over thirty years climate scientists have presented a range for climate sensitivity (ECS) that has hardly changed. It was 1.5-4.5°C in 1979 and this range is still the same today in AR5. The new report suggests that the inclusion of recent evidence, reflected in AR5, justifies a lower observationally-based temperature range of 1.25–3.0°C, with a best estimate of 1.75°C, for a doubling of CO2. By contrast, the climate models used for projections in AR5 indicate a range of 2-4.5°C, with an average of 3.2°C.

This is one of the key findings of the GWPF report Oversensitive: how the IPCC hid the good news on global warming, written by independent UK climate scientist Nic Lewis and Dutch science writer Marcel Crok. Lewis and Crok were both expert reviewers of the IPCC report, and Lewis was an author of two relevant papers cited in it.

In recent years it has become possible to make good empirical estimates of climate sensitivity from observational data such as temperature and ocean heat records. These estimates, published in leading scientific journals, point to climate sensitivity per doubling of CO2 most likely being under 2°C for long-term warming, with a best estimate of only 1.3-1.4°C for warming over a seventy year period.

“The observational evidence strongly suggest that climate models display too much sensitivity to carbon dioxide concentrations and in almost all cases exaggerate the likely path of global warming,” says Nic Lewis.

These lower, observationally-based estimates for both long-term climate sensitivity and the seventy-year response suggest that considerably less global warming and sea level rise is to be expected in the 21st century than most climate model projections currently imply.

“We estimate that on the IPCC’s second highest emissions scenario warming would still be around the international target of 2°C in 2081-2100,” Lewis says.

Full report: Short version

Long version: A Sensitive Matter: How The IPCC Buried Evidence Showing Good News About Global Warming 

via The Global Warming Policy Forum (GWPF)

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September 18, 2017 at 04:07PM

Catastrophic impacts of climate change can still be avoided, according to scientists who have admitted they were too pessimistic about the chances of limiting global warming.

The world has warmed more slowly than had been predicted by computer models, which were “on the hot side” and overstated the impact of emissions on average temperature, research has found.

New forecasts suggest that the world has a better chance than claimed of meeting the goal set by the Paris Agreement on climate change of limiting warming to 1.5C above pre-industrial levels.

The study, published in the prestigious journal Nature Geoscience, makes clear that rapid reductions in emissions will still be required but suggests that the world has more time to make the necessary changes.

Michael Grubb, professor of international energy and climate change at University College London and one of the study’s authors, admitted that his previous prediction had been wrong.

He stated during the climate summit in Paris in December 2015: “All the evidence from the past 15 years leads me to conclude that actually delivering 1.5C is simply incompatible with democracy.”

Speaking to The Times, he said: “When the facts change, I change my mind, as Keynes said.

“It’s still likely to be very difficult to achieve these kind of changes quickly enough but we are in a better place than I thought.”

Professor Grubb said that the new assessment was good news for small island states in the Pacific, such as the Marshall Islands and Tuvalu, which could be inundated by rising seas if the average temperature rose by more than 1.5C.

“Pacific islands are less doomed than we thought,” he said.

Professor Grubb added that other factors also pointed to more optimism on climate change, including China reducing its growth in emissions much faster than predicted and the cost of offshore wind farms falling steeply in the UK.

He said: “We’re in the midst of an energy revolution and it’s happening faster than we thought, which makes it much more credible for governments to tighten the offer they put on the table at Paris.”

The study found that a group of computer models used by the Intergovernmental Panel on Climate Change had predicted a more rapid temperature increase than had actually occurred.

The global average temperature has risen by about 0.9C since pre-industrial times but there was a slowdown in the rate of warming for 15 years before 2014.

Myles Allen, professor of geosystem science at the University of Oxford and another author of the paper, said: “We haven’t seen that rapid acceleration in warming after 2000 that we see in the models. We haven’t seen that in the observations.”

He said that the group of about a dozen computer models, produced by government research institutes and universities around the world, had been assembled a decade ago “so it’s not that surprising that it’s starting to divert a little bit from observations”.

He said that too many of the models used “were on the hot side”, meaning they forecast too much warming.

According to the models, keeping the average temperature increase below 1.5C would mean the world could afford to emit only about 70 billion tonnes of carbon after 2015. At the current rate of emissions, this so-called “carbon budget” would be used up in three to five years’ time.

Under the new assessment , the world can emit another 240 billion tonnes and still have a reasonable chance of keeping the temperature increase below 1.5C.

“That’s about 20 years of emissions before temperatures are likely to cross 1.5C,” Professor Allen said.

Full story

via The Global Warming Policy Forum (GWPF)

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September 18, 2017 at 03:45PM