To be certain sensitivity is still uncertain...

This is a follow-on from my earlier article about a new paper on climate sensitivity. It isn't a critique or analysis of the paper itself. Maybe other people will look at the work and how it differs from other sensitivity analysis. This is more about the reaction in the deniosphere with some of my meandering thoughts rolled in. I've been in two minds about whether to publish this because there are no firm conclusions. It's rather long-winded and a bit repetitive. But I don't feel like spending any more time editing it down. You can make of it what you will.

As you may know, the denialati are all over a new paper in Climate Dynamics by Nic Lewis and Judith Curry, who have taken a shot at estimating climate sensitivity. You can download a pre-publication pdf version here, together with supplementary information zipped here, courtesy Nic Lewis.

It's not at all odd that deniers would latch on to it when you think about it, even though the WUWT crowd variously "believe":

• Climate change isn't happening
• Climate change is always happening
• If the world is warming, it's not because of CO2 (ie climate sensitivity to CO2 is zero)
• There is no such thing as a greenhouse effect. The world is warmed by magic.
• The world is cooling
• We're heading for an ice age
• The increase in CO2 is not caused by humans (ie burning hydrocarbons doesn't release CO2)
• Atmospheric CO2 hasn't increased

One reason I say this isn't surprising is because even though the paper suggests the world is about to get a lot hotter, the authors argue a likelihood, or at least a possibility, that the surface may not get quite as hot, with a doubling of CO2, as a lot of other research suggests. This paper suggests that when CO2 hits 560 ppm later this century, Earth will at first be somewhere between 0.9°C and 2.5°C hotter than it was in the mid-1800s. And even if we stopped adding any more CO2 to the atmosphere at that point, temperatures would continue to rise, settling at between 1°C and 4°C hotter as the system approaches medium term equilibrium. None of which is by any means comforting. While these numbers extend almost to the same range as stated in the latest IPCC report (1.5°C to 4.5°C), it goes below the lower end of the IPCC most like range and doesn't hit the high end.

That's not quite an apples to apples comparison though. Lewis and Curry were looking at "effective" climate sensitivity which is not quite the same as equilibrium climate sensitivity. The difference as far as I can make out is as follows. "Effective" is on a centennial time scale whereas equilibrium is on a millenial time scale. "Equilibrium" refers to after the ice sheets stop melting and maybe even after the ocean circulation has stopped responding to climate change. The deep ocean circulation has a cycle of around a thousand years. Ice sheets can take several millenia to settle down after a climate forcing.

So all in all, the difference between Lewis and Curry and other estimates is one of a few tenths of a degree at most.

Did Judith Curry get a stadium wave reception in Denver?

Judith Curry boasted that she started a talk to American Physical Society Meeting in Denver with these words (archived here):

For the past 15+ years, there has been no increase in global average surface temperature

So she started off in her usual form, minus any uncertainty.  She then goes on to promote Marcia Wyatt's stadium wave, saying:

The stadium wave hypothesis provides a plausible explanation for the hiatus in warming and helps explain why climate models did not predict this hiatus. Further, the new hypothesis suggests how long the hiatus might last. 

Judith didn't write her full talk, but she put up some different options under a heading: "implications for the future":

Implications for the future: I. IPCC AR5 view

The hiatus will end soon, with the next El Nino
.
Implications for the future:  II.  View emphasizing natural internal variability

• The ‘hiatus’ will continue at least another decade
• Climate models are too sensitive to external forcing
• Hiatus persistence beyond 20 years would support a firm declaration of problems with the climate models
• Incorrect accounting for natural internal variability implies:
• —Biased attribution of 20th century warming
• —Climate models are not useful on decadal time scales

You can read her article here.  It seems to be a mix of mainstream science and fringe science (pattern seeking), such as: Climate shifts hypothesis:  synchronized chaos framework for natural internal variability (shift ca. 2001) as well as her protégé's stadium wave hypothesis.

Your prediction?

Anyway, what do you reckon. Is anyone up for a prediction? Will Judith's "hiatus" end sooner rather than later or will global surface temperatures continue to shuffle upwards very slowly for the next two decades? Can she sustain her "stadium wave" theory longer than this one that went for 15 minutes? You'll probably recall that back when she introduced the stadium wave to her readers Judith wrote:

“The stadium wave signal predicts that the current pause in global warming could extend into the 2030s,” Wyatt said, the paper’s lead author.

Now Judith has dropped back to maybe 2024, reducing it to only "at least another decade".

I'm game.  I don't think Marcia Wyatt's stadium wave will last another three years.  For one thing, it predicts that:

sea ice will recover from its recent minimum, first in the West Eurasian Arctic, followed by recovery in the Siberian Arctic,” Wyatt said. “Hence, the sea ice minimum observed in 2012, followed by an increase of sea ice in 2013, is suggestive of consistency with the timing of evolution of the stadium-wave signal 

So the stadium wave hypothesis will need to be heavily revised if either or both:

• global surface temperatures continue to rise in the coming few years 
• Arctic sea ice continues to disappear more each summer.

The next El Niño

Then there's El Niño.  I'm aware that ENSO predictions at this time of the year are fraught because, as BoM states on p3 of its latest ENSO report:

The predictability of El Niño or La Niña conditions for the period extending through and beyond autumn is lower than for forecasts made at other times of the year (known as “the autumn predictability barrier”). Long-range model outlooks should be used cautiously at this time.

Nevertheless, this is the first time in months there has been a POAMA chart like this one, which has been updated since the latest ENSO report on 24 February:

Source: Bureau of Meteorology

Jeff Masters at Wunderground.com recently wrote:

Two Pacific tropical storms form, boosting the odds of an El Niño

The atmospheric and oceanic conditions in the Equatorial Pacific are ripe for an El Niño event to develop this spring or summer. As detailed in a guest blog post by WSI's Dr. Michael Ventrice on February 21, all that is needed to trigger an El Niño this spring or summer are strong and persistent bursts of westerly winds in the Equatorial Pacific to help push warm water from the Western Pacific Warm Pool eastwards towards South America. Two tropical storms capable of doing just that formed in the Pacific on Friday, boosting the odds that we will see an El Niño event this spring or summer. 

Climate change in Denver

I'd also be curious as to how Judith's Denver audience reacted to her talk.  Colorado has been beseiged recently. Last year alone there were dreadful wildfires followed by the "biblical" flood.  Anyway, here are just four bits and pieces about how people in Denver and Colorado more generally are coping with and/or preparing for climate change.  There is lots more where these came from.

• Denver Water is performing the planning needed to adapt to potential water impacts from climate change...Still, there are a wide range of climate-change predictions for Colorado, which makes future water-supply planning difficult. 
• From AMWA: A simplified climate change scenario shows Denver’s [water] supply could be quite vulnerable to warming: a 2 to 5 degree Fahrenheit (1.1 - 2.8 degrees Celsius) increase in temperature could cause a 7 to 14% decline in water supply yield.
• The University of Colorado has a climate action plan.
• Chipotle says it could drop guacamole from its menu over climate change - Denver-based chain says it may have no choice.