mike

Guest commentary from Michelle L’Heureux, NOAA Climate Prediction Center

Much media attention has been directed at the possibility of an El Niño brewing this year. Many outlets have drawn comparison with the 1997-98 super El Niño. So, what are the odds that El Niño will occur? And if it does, how strong will it be?

To track El Niño, meteorologists at the NOAA/NWS Climate Prediction Center (CPC) release weekly and monthly updates on the status of the El Niño-Southern Oscillation (ENSO). The International Research Institute (IRI) for Climate and Society partner with us on the monthly ENSO release and are also collaborators on a brand new “ENSO blog” which is part of www.climate.gov (co-sponsored by the NOAA Climate Programs Office).

Blogging ENSO is a first for operational ENSO forecasters, and we hope that it gives us another way to both inform and interact with our users on ENSO predictions and impacts. In addition, we will collaborate with other scientists to profile interesting ENSO research and delve into the societal dimensions of ENSO.

As far back as November 2013, the CPC and the IRI have predicted an elevated chance of El Niño (relative to historical chance or climatology) based on a combination of model predictions and general trends over the tropical Pacific Ocean. Once the chance of El Niño reached 50% in March 2014, an El Niño Watch was issued to alert the public that conditions are more favorable for the development of El Niño.

Current forecasts for the Nino-3.4 SST index (as of 5 May 2014) from the NCEP Climate Forecast System version 2 model

More recently, on May 8th, the CPC/IRI ENSO team increased the chance that El Niño will develop, with a peak probability of ~80% during the late fall/early winter of this year. El Nino onset is currently favored sometime in the early summer (May-June-July). At this point, the team remains non-committal on the possible strength of El Niño preferring to watch the system for at least another month or more before trying to infer the intensity. But, could we get a super strong event? The range of possibilities implied by some models allude to such an outcome, but at this point the uncertainty is just too high. While subsurface heat content levels are well above average (March was the highest for that month since 1979 and April was the second highest), ENSO prediction relies on many other variables and factors. We also remain in the spring prediction barrier, which is a more uncertain time to be making ENSO predictions.

Could El Niño predictions fizzle? Yes, there is roughly a 2 in 10 chance at this point that this could happen. It happened in 2012 when an El Nino Watch was issued, chances became as high as 75% and El Niño never formed. Such is the nature of seasonal climate forecasting when there is enough forecast uncertainty that “busts” can and do occur. In fact, more strictly, if the forecast probabilities are “reliable,” an event with an 80% chance of occurring should only occur 80% of the time over a long historical record. Therefore, 20% of the time the event must NOT occur (click here for a description of verification techniques).

While folks might prefer total certainty in our forecasts, we live in an uncertain world. El Niño is most likely to occur this year, so please stay attentive to the various updates linked above and please visit our brand new ENSO blog.

Gavin provided a thoughtful commentary about the role of scientists as advocates in his RealClimate piece a few weeks ago.

I have weighed in with my own views on the matter in my op-ed today in this Sunday’s New York Times. And, as with Gavin, my own views have been greatly influenced and shaped by our sadly departed friend and colleague, Stephen Schneider. Those who were familiar with Steve will recognize his spirit and legacy in my commentary. A few excerpts are provided below:

[Read more…] about If You See Something, Say Something

My co-authors and I have just published an article in Nature Geoscience (advance online publication here; associated press release here) which seeks to explain certain enigmatic features of tree-ring reconstructions of Northern Hemisphere (NH) temperatures of the past millennium. Most notable is the virtual absence of cooling in the tree-ring reconstructions during what ice core and other evidence suggest is the most explosive volcanic eruption of the past millennium–the AD 1258 eruption. Other evidence suggests wide-spread global climate impacts of this eruption [see e.g. the review by Emile-Geay et al (2008)]. We argue that this–and other missing episodes of volcanic cooling, are likely an artifact of biological growth effects, which lead to a substantial underestimation of the largest volcanic cooling events in trees growing near treeline. We speculate that this underestimation may also have led to overly low estimates of climate sensitivity in some past studies attempting to constrain climate model sensitivity parameters with proxy-reconstructed temperature changes.

Tree rings are used as proxies for climate because trees create unique rings each year that often reflect the weather conditions that influenced the growing season that year. For reconstructing past temperatures, dendroclimatologists typically seek trees growing at the boreal or alpine treeline, since temperature is most likely to be the limiting climate variable in that environment. But this choice may also prove problematic under certain conditions. Because the trees at these locations are so close to the threshold for growth, if the temperature drops just a couple of degrees during the growing season, there will be little or no growth and therefore a loss of sensitivity to any further cooling. In extreme cases, there may be no growth ring at all. And if no ring was formed in a given year, that creates a further complication, introducing an error in the chronology established by counting rings back in time.
[Read more…] about Global Temperatures, Volcanic Eruptions, and Trees that Didn’t Bark

Guest commentary by Kevin Trenberth and John Fasullo

The hype surrounding a new paper by Roy Spencer and Danny Braswell is impressive (see for instance Fox News); unfortunately the paper itself is not. News releases and blogs on climate denier web sites have publicized the claim from the paper’s news release that “Climate models get energy balance wrong, make too hot forecasts of global warming”. The paper has been published in a journal called Remote sensing which is a fine journal for geographers, but it does not deal with atmospheric and climate science, and it is evident that this paper did not get an adequate peer review. It should not have been published.

The paper’s title “On the Misdiagnosis of Surface Temperature Feedbacks from Variations in Earth’s Radiant Energy Balance” is provocative and should have raised red flags with the editors. The basic material in the paper has very basic shortcomings because no statistical significance of results, error bars or uncertainties are given either in the figures or discussed in the text. Moreover the description of methods of what was done is not sufficient to be able to replicate results. As a first step, some quick checks have been made to see whether results can be replicated and we find some points of contention.

The basic observational result seems to be similar to what we can produce but use of slightly different datasets, such as the EBAF CERES dataset, changes the results to be somewhat less in magnitude. And some parts of the results do appear to be significant. So are they replicated in climate models? Spencer and Braswell say no, but this is where attempts to replicate their results require clarification. In contrast, some model results do appear to fall well within the range of uncertainties of the observations. How can that be? For one, the observations cover a 10 year period. The models cover a hundred year period for the 20th century. The latter were detrended by Spencer but for the 20th century that should not be necessary. One could and perhaps should treat the 100 years as 10 sets of 10 years and see whether the observations match any of the ten year periods, but instead what appears to have been done is to use only the one hundred year set by itself. We have done exactly this and the result is in the Figure..
[ed. note: italics below replace the deleted sentence above, to make it clearer what is meant here.]

SB11 appears to have used the full 100 year record to evaluate the models, but this provides no indication of the robustness of their derived relationships. Here instead, we have considered each decade of the 20th century individually and quantified the inter-decadal variability to derive the Figure below. What this figure shows is the results for the observations, as in Spencer and Braswell, using the EBAF dataset (in black). Then we show results from 2 different models, one which does not replicate ENSO well (top) and one which does (second panel). Here we give the average result (red curve) for all 10 decades, plus the range of results that reflects the variations from one decade to the next. The MPI-Echam5 model replicates the observations very well. When all model results from CMIP3 are included, the bottom panel results, showing the red curve not too dis-similar from Spencer and Braswell, but with a huge range, due both to the spread among models, and also the spread due to decadal variability.

Figure: Lagged regression analysis for the Top-of-the-atmosphere Net Radiation against surface temperature. The CERES data is in black (as in SB11), and the individual models in each panel are in red. The dashed lines are the span of the regressions for specific 10 year periods in the model (so that the variance is comparable to the 10 years of the CERES data). The three panels show results for a) a model with poor ENSO variability, b) a model with reasonable ENSO variability, and c) all models.

Consequently, our results suggest that there are good models and some not so good, but rather than stratifying them by climate sensitivity, one should, in this case, stratify them by ability to simulate ENSO. In the Figure, the model that replicates the observations better has high sensitivity while the other has low sensitivity. The net result is that the models agree within reasonable bounds with the observations.

To help interpret the results, Spencer uses a simple model. But the simple model used by Spencer is too simple (Einstein says that things should be made as simple as possible but not simpler): well this has gone way beyond being too simple (see for instance this post by Barry Bickmore). The model has no realistic ocean, no El Niño, and no hydrological cycle, and it was tuned to give the result it gave. Most of what goes on in the real world of significance that causes the relationship in the paper is ENSO. We have already rebutted Lindzen’s work on exactly this point. The clouds respond to ENSO, not the other way round [see: Trenberth, K. E., J. T. Fasullo, C. O’Dell, and T. Wong, 2010: Relationships between tropical sea surface temperatures and top-of-atmosphere radiation. Geophys. Res. Lett., 37, L03702, doi:10.1029/2009GL042314.] During ENSO there is a major uptake of heat by the ocean during the La Niña phase and the heat is moved around and stored in the ocean in the tropical western Pacific, setting the stage for the next El Niño, as which point it is redistributed across the tropical Pacific. The ocean cools as the atmosphere responds with characteristic El Niño weather patterns forced from the region that influence weather patterns world wide. Ocean dynamics play a major role in moving heat around, and atmosphere-ocean interaction is a key to the ENSO cycle. None of those processes are included in the Spencer model.

Even so, the Spencer interpretation has no merit. The interannual global temperature variations were not radiatively forced, as claimed for the 2000s, and therefore cannot be used to say anything about climate sensitivity. Clouds are not a forcing of the climate system (except for the small portion related to human related aerosol effects, which have a small effect on clouds). Clouds mainly occur because of weather systems (e.g., warm air rises and produces convection, and so on); they do not cause the weather systems. Clouds may provide feedbacks on the weather systems. Spencer has made this error of confounding forcing and feedback before and it leads to a misinterpretation of his results.

The bottom line is that there is NO merit whatsoever in this paper. It turns out that Spencer and Braswell have an almost perfect title for their paper: “the misdiagnosis of surface temperature feedbacks from variations in the Earth’s Radiant Energy Balance” (leaving out the “On”).

We were greatly saddened to learn that our revered colleague Stephen Schneider passed away this morning.

We are posting a personal account by Ben Santer of Steve’s amazing accomplishments and contributions. Ben’s account provides a glimpse into what made Steve so special, and why he will be so deeply missed:

Today the world lost a great man. Professor Stephen Schneider – a climate scientist at Stanford University – passed away while on travel in the United Kingdom.

Stephen Schneider did more than any other individual on the planet to help us realize that human actions have led to global-scale changes in Earth’s climate. Steve was instrumental in focusing scientific, political, and public attention on one of the major challenges facing humanity – the problem of human-caused climate change.

Some climate scientists have exceptional talents in pure research. They love to figure out the inner workings of the climate system. Others have strengths in communicating complex scientific issues to non-specialists. It is rare to find scientists who combine these talents.

Steve Schneider was just such a man.

Steve had the rare gift of being able to explain the complexities of climate science in plain English. He could always find the right story, the right metaphor, the right way of distilling difficult ideas and concepts down to their essence. Through his books, his extensive public speaking, and his many interactions with the media, Steve did for climate science what Carl Sagan did for astronomy.

But Steve was not only the world’s pre-eminent popularizer of climate science. He also made remarkable contributions to our scientific understanding of the nature and causes of climate change. He performed pioneering research on the effects of aerosol particles on climate. This work eventually led to investigation of how planetary cooling might be caused by the aerosol particles arising from large-scale fires generated by a nuclear war. This clear scientific warning of the possible climatic consequences of nuclear war may have nudged our species onto a different – and hopefully more sustainable – pathway.

Steve was also a pioneer in the development and application of the numerical models we now use to study climate change. He and his collaborators employed both simple and complex computer models in early studies of the role of clouds in climate change, and in research on the climatic effects of massive volcanic eruptions. He was one of the first scientists to address what we now call the “signal detection problem” – the problem of determining where we might expect to see the first clear evidence of a human effect on global climate.

After spending many years at the National Center for Atmospheric Research in Boulder, Steve moved to Stanford in 1996. At Stanford, Steve and his wife Terry Root led ground-breaking research on the impacts of human-caused climate change on the distribution and abundance of plant and animal species. More recently, Steve kept intellectual company with some of the world’s leading experts on the economics of climate change, and attempted to estimate the cost of stabilizing our planet’s climate. Until his untimely death, he continued to produce cutting-edge scientific research on such diverse topics as abrupt climate change, policy options for mitigating and adapting to climate change, and whether we can usefully identify levels of planetary temperature increase beyond which we risk “dangerous anthropogenic interference” with the climate system.

Steve Schneider helped the world understand that the burning of fossil fuels had altered the chemistry of Earth’s atmosphere, and that this change in atmospheric composition had led to a discernible human influence on our planet’s climate. He worked tirelessly to bring this message to the attention of fellow scientists, policymakers, and the general public. His voice was clear and consistent, despite serious illness, and despite encountering vocal opposition by powerful forces – individuals who seek to make policy on the basis of wishful thinking and disinformation rather than sound science.

Steve Schneider epitomized scientific courage. He was fearless. The pathway he chose – to be a scientific leader, to be a leader in science communication, and to fully embrace the interdisciplinary nature of the climate change problem – was not an easy pathway. Yet without the courage of leaders like Stephen Schneider, the world would not be on the threshold of agreeing to radically change the way we use energy. We would not be on the verge of a global treaty to limit the emissions of greenhouse gases.

It was a rare privilege to call Steve Schneider my colleague and friend. It was a privilege to listen to Steve jamming on his beloved 12-string guitar; to sing Bob Dylan songs with him. It was a privilege to share laughter, and good food, and a good glass of red wine. It was a privilege to hear his love of science, and his deep passion for it.

We honor the memory of Steve Schneider by continuing to fight for the things he fought for – by continuing to seek clear understanding of the causes and impacts of climate change. We honor Steve by recognizing that communication is a vital part of our job. We honor Steve by taking the time to explain our research findings in plain English. By telling others what we do, why we do it, and why they should care about it. We honor Steve by raising our voices, and by speaking out when powerful “forces of unreason” seek to misrepresent our science. We honor Steve Schneider by caring about the strange and beautiful planet on which we live, by protecting its climate, and by ensuring that our policymakers do not fall asleep at the wheel.

Ben Santer