Frequently Asked Questions

What is Berkeley Earth?

Berkeley Earth was founded in early 2010 with the goal of addressing the major concerns of skeptics regarding global warming and the land surface temperature record.

We have several major objectives for our continuing work. We plan further scientific investigations on the nature of climate change, a major education and communications program to strengthen the scientific consensus on global warming, and work to reduce greenhouse gas emissions in the places that will be the worst emitters over the next 30 years. One key element of this latter program will be to try to forge a new coalition between industry and environmental groups for the use of cleanly-produced natural gas as a bridging fuel to slow global warming over the next few decades – with a particular focus on China.

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Why is the work being done by Berkeley Earth important?

Existing data used to show global warming have met with much criticism. Berkeley Earth attempts to resolve current criticism of the former temperature analyses by making available an open record to enable rapid response to further criticism and suggestions. Our results include our best estimate for the global temperature change and our estimates of the uncertainties in the record.

We believe that science is nonpartisan and our interest is in getting a clear view of the pace of climate change in order to help policy makers to evaluate and implement an effective response. In choosing team members, we engage people whose primary interests are finding answers to the current issues and addressing the legitimate concerns of the critics on all sides. None of the scientists involved has taken a public political stand on global warming.

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Why has Berkeley Earth published in GIGS?

Berkeley Earth published several papers in the SciTechnol journal Geoinformatics and Geostatistics: An Overview (GIGS) primarily because:

  1. We liked their emphasis on statistics. Berkeley Earth uses modern and advanced statistics in several of our papers, and we know that experts in climate change are not necessarily the best people to evaluate novel statistical approaches.
  2. We felt that it was important to publish in a journal that would provide open access to the public. The vast majority of the public cannot easily access “reader-pays” journals — and openness and transparency are core principles of Berkeley Earth. For this reason, we have only submitted our papers to journals that provide open and free access to all. Manuscripts accepted by GIGS are not subject to any page/color charges, or article processing charges, so nor can it be considered a “author-pays” journal.
  3. We liked their quick turn around time. We had been frustrated with the time it took to get some of our other papers reviewed, and liked the idea of a turn around in a matter of weeks.

Additionally, before submission of our paper, we asked several esteemed scientific peers about their experiences with SciTechnol, and learned that their experiences were largely positive. We therefore decided to submit our paper to GIGS, despite its being a new journal.

For each of our papers submitted to GIGS, we received 3 detailed peer reviews from experts in the field. These reviews were helpful, and demonstrated that the reviewers had a strong understanding of the content of our papers. We incorporated their feedback, which we believe improved the papers substantially, and these changes are reflected in the final versions that are published by GIGS.

In July 2012, when we first posted our draft papers online for public comment, we stated that the paper had been submitted to JGR for journal peer review (JGR required this statement). However, some time later, we heard back from the editor at JGR that they would not consider the submission of our results paper (or even send it to their peer reviewers) until after our “methods” paper had been published. The much more detailed methods paper was delayed unreasonably, we believe, because of its departure from traditional methods and its statistical complexity. Referee comments from the initial submission to JGR did not uncover any significant errors although they asked for many worthwhile clarifications (largely because the mathematic techniques, although standard to statisticians, were new to them) that held back the acceptance. We responded to the editor, arguing that this requirement was unusual and ill conceived. We can point to a vast number of papers with results that were published prior to the kind of detailed analysis of methods that we were being required to produce. In fact, the results paper was written to be able to stand alone; it contains all that is needed. Nevertheless, JGR refused to forward our paper for peer review, so we never received any comments from the JGR referees on the results paper. Delaying submission to JGR until after the methods paper was accepted would almost certainly have excluded the Berkeley Earth work from the next IPCC report. So we began searching for a journal with open access, quick turn around time, and a good grasp of modern statistics — and finally settled on GIGS.

Our experience with GIGS has been extremely positive. Not only were the peer reviews helpful, but they demonstrated a strong understanding of the material. The total process (including submission, getting comments from the reviewers, making the changes, resubmitting, acceptance, and then publication) took about 3 months. We expect most important articles will be published in similar open online journals in the not-too-distant future — we certainly hope to submit more papers to GIGS.

Some people think that peer review consists of submitting a paper to a journal and waiting for the anonymous comments of referees. Traditional peer review is much broader than that and much more open. In science, when you have a new result, your first step is to present it to your colleagues by giving presentations, talks at local and international conferences, colloquia, and by sending out “preprints”. Such traditional and open peer review has many advantages. It usually results in better papers in the archival journals, because the papers are widely examined prior to publication. All of the Berkeley Earth papers were thoroughly peer reviewed prior to being posted on our website. We welcome the additional review of anonymous journal referees (and indeed, agree that this is still an important gateway to ensure that all papers have a minimum of reviews) — but we feel that our work should be judged primarily on the statistical approach used and the transparency of our analysis — not on the fact that we have been published in a peer reviewed journal.

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Who is carrying out this work?

Berkeley Earth is headed by Elizabeth Muller and Richard Muller, the father/daughter team that founded Berkeley Earth. The main scientific work is carried out by Robert Rohde. Richard Muller is a Professor of Physics at the University of California at Berkeley, Faculty Senior Scientist at the Lawrence Berkeley Laboratory, and President of Muller & Associates LLC. Robert Rohde is a scientist who obtained his PhD in experimental/theoretical physics at the University of California at Berkeley. His expertise includes the analysis of large data sets, with estimates of statistical and systematic effects. Together, Richard and Robert have co-authored a series of papers on the analysis of bio diversity in the fossil record.

View a full list of the our team members.

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What is Berkeley Earth's co-founder Richard Muller's prior expertise in climate?

Richard Muller’s published works on climate have appeared in some of the most prestigious peer-reviewed journals including:

  1. Science (vol. 277, pp 215-218, 11 July 1997; vol. 288, p 2143-2144, 23 June 2000).
  2. Proceedings of the US National Academy of Sciences (vol. 94, pp 8329-8334, Aug 5, 1997).
  3. Geology (vol. 25, pp. 3-6, 1997; vol. 25, pp. 859-861, 1997).
  4. Paleoceanography (vol. 17, pp. 2-1 to 2-12, 2002).
  5. Geoch. Cosmochim. Acta (vol. 67, pp 751-763, 2003).
  6. Nature (vol.377, pp 107-108, 14 September 1995).

and also in other journals such as Eos. He has been active in the American Geophysical Union on climate research, and wrote “Ice Ages and Astronomical Causes”, a technical book published by Springer.

Richard was also deeply involved in the hockey stick issue, and was a named referee chosen to review the report of the National Research Council of the US National Academy of Sciences.

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What exactly has Berkeley Earth done so far?

The latest results from Berkeley Earth are available here. Several of our scientific papers have now been published, and we have made our data and analysis programs freely available to the public.

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How did Berkeley Earth come about?

Berkeley Earth was created in 2010, by Richard Muller and his daughter Elizabeth Muller who had been previously collaborating on energy and climate issues. Together they observed a real need for a new project to analyze current global surface temperature records in order to respond to concerns of critics and calm the debate about global warming. After joining with lead scientist Robert Rohde, Berkeley Earth was created. In early 2013, Berkeley Earth became a new, independent non-profit.

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Who is funding Berkeley Earth?

A complete list of our donors and the amounts that they contributed is available here.

Donations were primarily provided as unrestricted educational grants and donors have no influence over our methodology or our published results. Our results are public, have been presented with full transparency, and our data and programs are available to those who wish to carry out their own analysis.

A statement from the Charles Koch Foundation on the Berkeley Earth research is available here.

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It appears that Berkeley Earth's analysis shows a temperature rise greater than others had previously published. Is this so? Can you explain?

Most Berkeley Earth plotted data is land only. Land warms more than oceans, so when we include the ocean we expect the total global warming to be less.

We started with the land data for a couple reasons:

  1. It is the data that is most greatly affected by the most contentious issues: data selection bias, urban heat island, and station integrity issues. These are major concerns that we wanted to address.
  2. With 1.6 billion measurements, culling land temperature data was a major effort. It made sense to divide the analysis into two stages.

The temperature rise on land is greater than in the oceans, greatly due to the oceans distribution of heat over the mixed layer thereby reducing the temperature rise. Because land keeps the heat mostly on the surface, the land temperature is actually more sensitive to greenhouse gases than is the world temperature.

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Is CO2 leading or lagging temperature rise?

Data from ice core records strongly suggest that the prehistoric carbon dioxide changes were largely a response, not a cause, of temperature changes. This is not a surprise, since warm weather makes CO2 less soluble in water. In fact, a 800-year lag has been reported, and this is consistent with the known fact that it takes about 800 years for the ocean to overturn, that is, for all of the deep sea water to migrate to the surface where it can give up its dissolved carbon dioxide.

However, for the past century we know that the CO2 is not coming from the oceans but from human burning of fossil fuels. We can tell this from C-14 in the atmosphere, also known as radiocarbon. Seawater has high radiocarbon; fossil fuels have none. The increased CO2 in the atmosphere matches the low radiocarbon value of fossil fuel, not the high value from CO2 dissolved in seawater. In addition, we know how much fossil fuel has been converted into CO2, and there is more than enough to account for the atmospheric increase. In fact, we can determine that much, nearly half, of the emissions are dissolving into sea water and being absorbed by plants. So it is clear that it is the CO2 that comes first, not the warming.

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Has Global Warming Stopped?

Some people have suggested that there has been no global warming over the past 13 years, and they ask whether our land-only analysis verifies that. The graph shows the results of our analysis with 1-year averaging (to smooth it). The black curve is the result of our analysis, and the grey lines represent our 95% confidence limits.

The large fluctuations up and down that take place every few years correlatevery strongly with the North Atlantic temperatures (the AMO index) and withEl Nino (ENSO index 3.4). See our paper on “Decadal Variations in the Global Atmospheric Land Temperatures” for analysis of that. The presence of these fluctuations makes any strong extrapolations from short-term behavioruncertain.


Some people draw a line segment covering the period 1998 to 2010 and arguethat we confirm no temperature change in that period. However, if you didthat same exercise back in 1995, and drew a horizontal line through the datafor 1980 to 1995, you might have falsely concluded that global warming hadstopped back then. This exercise simply shows that the decadal fluctuationsare too large to allow us to make decisive conclusions about long termtrends based on close examination of periods as short as 13 to 15 years.

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What is new about the statistical approach used?

The central challenge of global temperature reconstruction is to take spatially and temporally diverse data exhibiting varying levels of quality and construct a global index series that can track changes in the mean surface temperature of the Earth. This challenge presents no easy solution and we believe that there is inherent value in comparing different approaches to this problem as well as understanding the weaknesses intrinsic to any given approach. Thus, we have studied both the existing methodologies for averaging and homogenizing data as well as look for new approaches whose features seem to incorporate valuable alternatives to the existing methods.

The statistical methods that we use have been developed by Robert Rohde in close collaboration with David Brillinger, a Professor of Statistics at the University of California at Berkeley, and the other team members. They include the statistical approach called Kriging (a process which allows us to combine fragmented records in an optimum way), the scalpel (which identifies discontinuities and cuts the data at those points) and weighting (in which the program estimates numerically the reliability of a data segment and applies a weight that reduces the contribution of the poor samples). The methods all use raw data as input. There are no manual corrections applied; all the weights and scalpel points are determined using automated and reproducible methods.

Our algorithms aim to:

  1. Make it possible to exploit relatively short (e.g. a few years) or discontinuous station records. Rather than simply excluding all short records, we prefer to design a system that allows short records to be used with a low – but non-zero – weighting whenever practical.
  2. Avoid gridding. All three major research groups currently rely on spatial gridding in their averaging algorithms. As a result, the effective averages may be dependent on the choice of grid pattern and may be sensitive to effects such as the change in grid cell area with latitude. Our algorithms eliminate explicit gridding entirely.
  3. Place empirical homogenization on an equal footing with other averaging. We distinguish empirical homogenization from evidence-based homogenization. Evidence-based adjustments to records occur when secondary data and/or metadata is used to identify problems with a record and to then propose adjustments. By contrast, empirical homogenization is the process of comparing a record to its neighbors to detect undocumented discontinuities and other changes. This empirical process performs a kind of averaging as local outliers are replaced with the basic behavior of the local group. Rather than regarding empirical homogenization as a separate preprocessing step, we plan to incorporate empirical homogenization as a process that occurs simultaneously with the other averaging steps.
  4. Provide uncertainty estimates for the full time series through all steps in the process.

A detailed description of the statistical methods used by Berkeley Earth can be found in our “Methods” paper.

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There have been many criticisms of station quality. How can you be sure your results will be reliable if you are including stations that do not meet NOAA's criteria for station quality?

One of the elements that we have analyzed is temperature records from only the very best sites (as classified by Anthony Watts and his team) contrasted with the poorer sites. This analysis is in the paper “Earth Atmospheric Land Surface Temperature and Station Quality in the United States”, available here.

Additionally, each of our 39,028 sites has been classified as urban or rural using the map published by the Modis satellite team, and have also used that classification to look for differences. The results of that analysis are in the paper “Influence of Urban Heating on the Global Temperature Land Average”, available here.

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Does Berkeley Earth use adjusted data?

Berkeley Earth collects data from 16 different sources. Wherever a source has an unadjusted version, that version is used. If multiple data sources have records for the same location, unadjusted values are given priority over adjusted values.

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Does Berkeley Earth homogenize data?

Other groups such as NASA, NOAA, and the Hadley Center either work with data that has been homogenized or they make homogenizing adjustments to the data series. In the Berkeley method station records are not adjusted up or down. Rather, stations that display unreliable data characteristics are down weighted in the construction of spatial temperature fields. Stations that show evidence of undocumented moves or instrument change (e.g. evidenced by extremely abrupt changes, either up or down) are split at the change point and treated as two separate records.

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Is the urban heat island (UHI) effect real?

The Urban Heat Island effect is real. Berkeley’s analysis focused on the question of whether this effect biases the global land average. Our UHI paper analyzing this indicates that the urban heat island effect on our global estimate of land temperatures is indistinguishable from zero.

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How does Berkeley data differ from other global temperature estimates?

Other major global land temperature reconstructions by NASA, NOAA, and the Hadley Center largely rely on the same set of monthly data from about 7,000 stations that comprise the Global Historical Climatological Network (GHCN-M). Berkeley makes use of data from over 36,000 stations. For any given month after 1880, the Berkeley dataset has between 2 times and 8 times the number of stations with data available compared to GHCN-M. Prior to 1880 Berkeley has about 20 to 50 percent more station records available for any given month.

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Why didn't Berkeley Earth wait for peer review?

Some people think that peer review consists of submitting a paper to a journal and waiting for the anonymous comments of referees. Traditional peer review is much broader than that and much more open. In science, when you have a new result, your first step is to present it to your colleagues by giving presentations, talks at local and international conferences, colloquia, and by sending out “preprints.” In fact, every academic department in the sciences had a preprint library where people would read up on the latest results. If they found something to disagree with, they would talk to or write the authors. Preprint libraries were so popular that, if you found someone was not in the office or lab, the first place you would search would be in the preprint library. Recently these rooms have disappeared, their place taken over by the internet. The biggest preprint library in the world now is a website,

Such traditional and open peer review has many advantages. It usually results in better papers in the archival journals, because the papers are widely examined prior to publication. It does have a disadvantage, however, that journalists can also pick up preprints and report on them before the traditional peer-review process is finished.

Perhaps because of the media picking up on talks and preprints, a few journals made a new rule: they will not publish anything that is distributed as a preprint or that is discussed openly in a meeting or colloquium. This policy has resulted in more attention to several journals, but the restrictive approach had a detrimental effect on the traditional peer review system. Some fields of science, for example String Theory, objected so strongly that they refuse to publish in these journals, and they put all their papers online immediately.

The best alternative would be to have the media hold back and not report preprint material. Unfortunately they refuse to do that. The situation is made more difficult by the fact that many of the media misreport the content of the preprints. For that reason Berkeley Earth has tried to answer the questions given to us by the media, in hopes that our work will be more accurately reported. The two page summary of findings is also meant to help ensure that the media reports accurately reflect the content of our papers.

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Is it time now to end global warming skepticism?

In its first phase, Berkeley Earth addressed the concern: was the temperature rise on land improperly affected by the four key biases (station quality, homogenization, urban heat island, and station selection)? The answer turned out to be no, but they were questions worthy of investigation.

Berkeley Earth has now found that the best explanation for the warming seen over the past 250 years is human greenhouse gas emissions. While this does not prove that global warming is caused by greenhouse gas emissions, it does set the bar for alternative explanations.

Berkeley Earth has not addressed issues of satellite data, tree ring and proxy data, or climate model accuracy. Scientists at Berkeley Earth remain skeptical of many elements of “climate change” – including attribution of hurricanes, tornadoes, and other extreme weather events to global warming.

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What is next for Berkeley Earth?

We have several major objectives for our continuing work. We plan further scientific investigations, a major education and communications program, and a program to analyze technologies and policies related to greenhouse gas emissions, with emphasis on affordable technologies for countries that are expected to be rapidly industrializing over the next 30 years. One key element of this latter program will be to try to forge a new coalition between industry and environmental groups for the use of cleanly-produced natural gas as a bridging fuel to slow global warming over the next few decades – with a particular focus on China.

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Do you have a newsletter? How can I stay up to date with Berkeley Earth's ongoing work?

You can sign up for Berkeley Earth email alerts here.

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Is there a reuse policy for using information and media presented by Berkeley Earth?

The authors of the material available on the Berkeley Earth website ( grant permission (free of charge) to authors, readers and third parties to reproduce their materials as part of another publication or entity with proper sourcing to Berkeley Earth and by additionally providing a link to the Berkeley Earth website ( ).

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