Major remaining questions are why the Earth warmed, if it will continue warming, and what the effects are

Researchers at the University of California, Berkley, have just completed a massive review of collected climatology data and have concluded that despite imperfections -- namely, massive local discrepancies, the overall conclusions of major climate studies were correct -- the Earth has warmed.

UC Berkley dubs the study the Berkley Earth Surface Temperature study -- or "BEST" for short.

I. What is BEST?

The BEST project was carried out by Robert Rohde, Robert Jacobsen, Richard A. Muller, Saul Perlmutter, Arthur Rosenfeld, Charlotte Wickham, Jonathan Wurtel, who at the time were all associate with UC Berkley; Judith Curry a researcher at the Georgia Institute of Technology; and Donald Groom a researcher at the Lawrence Berkley National Laboratory.

Interestingly, while the group of researchers completed four papers on the work... ... they did not wait for these papers to be peer-reviewed and published, before calling attention to the work.  Rather, they made the unusual step of publishing most of their analysis code (sans apparently some analysis scripts); their data sets used in the analysis; and plots and graphs of their conclusions.

Depending on who you ask, this approach is either an attempt to create a media circus prior to peer review or an unusual but good-hearted attempt to allow the non-expert public to participate in peer-review.

II. The Earth has Warmed, the Pope is Catholic

Aside from quesitons of how the data was published, the critical question is -- what does the study claim?  Well it explicitly only covers land data -- no sea data.  Basically it concludes using 15 compiled data sets, which date back to 1800, that a 1ºC warming has occurred since the mid-1950s.  

Some of the data in this study was taken from Global Historical Climatology Network, administered by National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Center (NCDC) -- a source of data also used in past studies by the NOAA, NASA, and the Hadley Center.  But the entire data set is more than five times as big as any other study, encompassing 39,000 weather stations.  Thus the study isn't entirely independent from past results, but does offer some fresh blood.

The data indicates two things, one of which the press releases glosses over.

1. The Earth does appear to have warmed.
2. Warming appears to have hit a standstill since 2000.

The second point is disguised as most of the initial press releases focus on a decadal averaged figure.  Since the late 1990s were a period of net increase, they make the first part of the 2000s also look like a period of increase when the decadal rolling average is applied.  The real picture is seen below:
Berkley heat levels
Note the relative flat line over the last decade, which is eye-catching, even if you discount the steep decline in 2010.  Now witness how this contrasts with the trend over the last decade in the rolling average shown in the press release:

Berkley rolling average seems unfortunate that the misleading rolling average was selected of these two figures.  This chart conveys what appears to be one accurate piece of information to the reader -- that the temperature has warmed over the last half century, but also conveys an inaccurate impression that warming has continued over the last decade.

III. Of Urban Heat Islands and Averages

One of the paper's key objectives seems to be to cast this new work as an unbiased analysis that takes into account past criticisms.

Elizabeth Muller, co-founder and Executive Director of Berkeley Earth, comments, "[This work will] cool the debate over global warming by addressing many of the valid concerns of the skeptics in a clear and rigorous way."

Notably, the paper seems to give special interest to discussing the urban heat island (UHI) effect, which is consistently raised by Anthony Watts as an underaddressed source of error.  The UHI premise is that stations near cities are "worse" than their rural counterparts, as local heat from the city can give erroneous readings.

The study offers some analysis of this hypothesis, offering that the "worst" stations had the same climate pattern as those that were ranked "okay" (for reasons unknown the "worst" stations were not compared to the "best" stations).  It concludes that the UHI was "locally large and real", but asserts that it does not significant effect the overall conclusion because urban areas only account for 1 percent of total surface area on Earth.

Unfortunately, if the author's intent in this analysis was to placate Mr. Watts, a seasoned and respected skeptic, they only halfway succeeded.

Mr. Watts comments, "The unique BEST methodology has promise. The scalpel method used to deal with station discontinuity was a good idea and I’ve said so before."

But more critically he adds:

They didn’t adequately deal with that 1% [urban area] in my opinion, by doing a proper area weighting. And what percentage of weather stations were in that 1%? While they do have some evidence of the use of a "kriging" technique, I'm not certain is has been done properly. The fact that 33% of the sites show a cooling is certainly cause for a much harder look at this. That's not something you can easily dismiss, though they attempt to. This will hopefully get sorted out in peer review.

IV. What the Study Does Not Show

The study makes no attempt to explain the source of warming.  In short it supports the global warming hypothesis, but does not majorly support or deny the anthropogenic global warming (AGW) hypothesis.

In fact it offers possibilities that could support or repudiate AGW, writing.  Namely it comments that the Atlantic Multidecadal Oscillation (AMO) -- sea current/salt flow is strongly correlated with land temperature shifts.  The source of this correlation is unclear, it comments.  It might be naturally occurring, or it could hypothetically be manmade.

Describes UC Berkley:

Such changes may be independent responses to a common forcing (e.g. greenhouse gases); however, it is also possible that some of the land warming is a direct response to changes in the AMO region. If the long-term AMO change have been driven by greenhouse gases then the AMO region may serve as a positive feedback that amplifies the effect of greenhouse gas forcing over land.  On the other hand, some of the long-term change in  the AMO could be driven by natural variability, e.g. fluctuations in thermohaline flow. In that case the human component of global warming may be somewhat overestimated.

In other words, correlation does not prove causation, though causation may hold true; and further the driver of the correlation (man? nature?) is unknown.  Got it?

Despite the study being relatively agnostic on the topic of AGW, that didn't stop some news outlets from taking the opportunity to lash out at AGW skeptics.  Forbes' guest columnist Peter Gleick bitterly comments, "Indeed, even most remaining climate change skeptics and deniers have moved away from saying there is no warming. Now, their major talking points are that it isn't caused by humans, or only a little bit, or it won’t be bad, or we can’t afford to fix it, or… Denial is a moving target."

Of course this conclusion seems odd.  While there may be some disingenous skeptics who profited off arguing that globally warming in all contexts was proven untrue -- much as at least one AGW advocates turned his unfounded claims of AGW being proven completely true into a near billion dollar fortune and a Nobel Peace Prize -- many AGW skeptics -- like many AGW advocates -- took a balanced approach calling for more research.

Other critical articles took a similar heavy-handed approach, at some points spewing blatant factual inaccuracies.  States Jess Zimmerman, an armchair analyst at enviroblog Grist, "The Arctic now has ice-free summers, 90 years in advance of predictions."

Grist error

Of course this ice free winter is a bit like a unicorn -- it hasn't been recently observed, though some -- like Ms. Zimmerman -- mistakenly believe it has.  

Walt Meier, a research scientist at the University of Colorado's National Snow and Ice Data Center kindly corrected the errant blogger, writing, "The statement "The Arctic now has ice-free summers, 90 years in advance of predictions." is most definitely flat-out wrong. The Arctic has not had less than 4 million square kilometers, in our data and any other source one cares to look at, even at the summer minimum.While extent and thickness are decreasing and ice-free summers are certainly possible, even probable, in much less than 90 years, we are not there yet. Not even close."

Ice Cover
Look -- there's ice in the summer! [Source: NOAA/NASA]

Sadly his veteran voice has thus far been ignored by the Grist writer, and the piece remains uncorrected.

V. Conclusions

This new research clearly was a thoughtful, if less than definitive look at warming.  

It arguably has some flaws.  It received major criticism from a math professor for its use of smoothing, and we think its prominent positioning of the decadal analysis versus the more revealing year-by-year plot is slightly misleading.  

That said, while some of its techniques and presentations could be criticized, overall the work(s) offer(s) a lot of interesting information to the public.

The research shows that indeed the Earth warmed, but where it's going -- particularly after a decade of virtually no warming -- remains to be seen.

Amid this backdrop, it's important to remind the reader that the cause of historical warming in the 1960-2000 period is absolutely not known definitively.  AGW advocates and skeptics alike are disingeneous to suggest otherwise.  Further, even if AGW does happen to be real, how mankind would be increasing the temperature rise (Greenhouse gases? Landuse changes? Black carbon on snow? Dark colored aerosols?)

And most importantly, the question of the overall effects of potential future warming on human society are unclear.  Will warming help mankind?  Will it hurt it?  It's hard to say at this point, though various studies have claimed both benefits and dangers of a potentially warming planet.

As for these questions, UC Berkley is largely disinterested in answering them -- at least immediately.  Rather, it's more interested in conducted a thorough analysis of sea station data.  When it does come out with this analysis, we'll likely be in for another wave of AGW theory supporters bashing the skeptics, and some skeptics bashing right back, both claiming the data supports their claims in some way.

Those interested in unbiased answers will simply have to review the commentary -- and the works themselves -- and try to glean the true picture.

Source: Berkley Earth

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