steve.schulin - Calamitology.com

March 30, 2009

Bejing data shows "Radiative forcing is mainly caused by aerosol particles"

Source: Wang, Y., H. Che, J. Ma, Q. Wang, G. Shi, H. Chen, P. Goloub, and X. Hao (2009), Aerosol radiative forcing under clear, hazy, foggy, and dusty weather conditions over Beijing, China, Geophys. Res. Lett., 36, L06804, doi:10.1029/2009GL037181.

The following figure shows that particles in the atmosphere tend to cool the surface and warm the atmosphere:

Figure 3. Aerosol radiative forcing at the surface, TOA, and in the atmosphere under clear, hazy, foggy, and dusty weather conditions.

The values shown here are just part of the story. Marc Jacobson of Stanford, for example, has described why particles in the atmosphere do tend to warm the atmosphere day and night, and to cool the surface during the day. But at night, the particles tend to have a warming effect on the surface.

December 28, 2008

Global cooling forecast by Klyashtorin and Lyubushin

For some years, I've read fisheries researcher Dr. Gary Sharp's admiring descriptions of the climate science scholarship of a pair of Russian researchers -- Leonid Klyashtorin and Alexey Lyubushin. Today, I learned that the English version of their 2007 book "Cyclic Climate Changes and Fish Productivity" is freely available as pdf file at

http://alexeylyubushin.narod.ru/Climate_Changes_and_Fish_Productivity.pdf

Dr Sharp served as their English editor, and the body of English-language scientific literature is richly enhanced by this addition. The book contains much that Dr. Sharp has already synthesized in his 2003-vintage UN FAO Technical Paper No. 452 ("Future climate change and regional fisheries: a collaborative analysis"), the full pdf of which is also freely available on the web, via the abstract page at

http://www.fao.org/DOCREP/006/Y5028E/Y5028E00.HTM

September 15, 2008

Thermocephaly

I took the liberty of registering a new domain name this morning -- thermocephaly.com -- after seeing it used in an essay by Prof. Joel M. Kauffman [Climate Change Reexamined. Journal of Scientific Exploration 21(4)723-749, 2007]. The paper is freely available here. Dr. Kauffman discusses a pretty wide range of interesting topics of interest to anybody who smiles or frowns at the mention of the word calamitology. One of the subjects that was especially interesting to me was his discussion of the literature which contradicts the notion that today's atmospheric CO2 levels are at levels unseen in a long time. [Note to Prof. Kauffman: if you'd like, I'd be happy to transfer the registration of thermocephaly.com to you or your designee. And thank you again for your enthusiastic comments about my candidacy and calamitology.com. If you know any folks here in the Maryland suburbs of DC, I'd appreciate if you'd let them know that I'm running for Congress here in the 4th District. The incumbent's position statement and policy recommendation for mandatory CO2 emissions controls are part of why I'm running against her.]

September 13, 2008

Decadal-scale (and longer and shorter) variation: solar dimming and brightening

Kawamoto and Hayasaka, of Japan, have an interesting new Geophysical Research Letters paper analyzing Chinese data. [Kawamoto, K., and T. Hayasaka (2008), Relative contributions to surface shortwave irradiance over China: A new index of potential radiative forcing, Geophys. Res. Lett., 35, L17809, doi:10.1029/2008GL035083.]

Here's how they introduce the subject: "The surface shortwave irradiance (S) received by the Earth's surface drives climate-system changes through dynamical, thermodynamical, and radiative processes. Scattering and absorption by air molecules, aerosols, and cloud particles influence S before it reaches the surface. Because the effects of these factors vary temporally and spatially, S shows large variability at different time scales.

"Previous studies have reported that S decreased for several decades before around 1990 but then began to increase (so-called the solar dimming and brightening), although observation points were limited [e.g., Gilgen et al., 1998; Stanhill and Cohen, 2001; Wild et al., 2005]. The reason for this long-term variation is still unclear and is the subject of active discussion. For example, reports of decreased S between 1960 and 1990 appear contradictory to decreasing trends in cloud amount found by ground measurements over most parts of China [Qian et al., 2006], assuming that other atmospheric parameters remained the same. Meanwhile, large quantitative differences still exist in S produced by simulations of radiative forcing including anthropogenic aerosols and observed S [Takemura et al., 2005]. Given this background, a new index that represents the sensitivities of S to changes in related factors such as clouds, aerosols, and water vapor should be useful, since S variability can then be estimated from observed changes in related factors."

"... Shortwave irradiance (0.2–5 μm considered in this study) is influenced by various factors, including clouds, aerosols, water vapor, and surface albedo, according to the solar incidence of the considered point."

The abstract, and subscriber or pay-per-view link to full text is available here

The references cited in the above are:

* Gilgen, H., M. Wild, and A. Ohmura (1998), Means and trends of shortwave incoming radiation at the surface estimated from Global Energy Balance Archive data, J. Clim., 11, 2042–2061.

* Stanhill, G., and S. Cohen (2001), Global dimming: A review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences, Agric. For. Meteorol., 107, 255–278.

* Wild, M., et al. (2005), From dimming to brightening: Decadal changes in solar radiation at Earth's surface, Science, 308, 847–850.

* Qian, Y., P. Kaiser, R. Leung, and M. Xu (2006), More frequent cloud-free sky and less surface solar radiation in China from 1955–2000, Geophys. Res. Lett., 33, L01812, doi:10.1029/2005GL024586.

* Takemura, T., T. Nozawa, S. Emori, Y. Nakajima, and T. Nakajima (2005), Simulation of climate response to aerosol direct and indirect effects with aerosol transport-radiation model, J. Geophys. Res., 110, D02202, doi:10.1029/2004JD005029.

September 12, 2008

A closer look at top-of-atmosphere radiation data on reflected solar (shortwave) and emitted thermal (longwave)

Loeb et al. have a new paper in press at Journal of Climate [Towards Optimal Closure of the Earth's Top-of-Atmosphere Radiation Budget, doi: 10.1175/2008JCLI2637.1]. One of the co-authors is Bruce Wielicki, a colleague of Loeb's at NASA Langley Research Center, in Hampton, Virginia. Dr. Wielicki was the lead author of a 2002 paper which caused quite a stir [Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget, Science 295: 841-844 (1 Feb 2002)].

The new paper doesn't seem likely to cause the same kind of public stir, and part of that is because it is quite understated in the way it expresses its conclusions. But there are some clear indications that the new findings will indeed cause a stir amongst those radiative forcing scholars who claim the science is settled enough.

For example, the new study pegs global mean CERES SW TOA flux as 99.5 Wm-2. That's markedly different than the 107 Wm-2 in Trenberth (1997).

The new study pegs global mean LW TOA flux as 239.6 Wm-2. That's markedly different than the 234 Wm-2 in Trenberth (1997).

To put these numbers in perspective, it is fair to remember that the alarmists have long been claiming to see the "fingerprint" of a calculated forcing of 2.4 Wm-2 -- that was the cumulative GHG forcing over more than a century reported by IPCC in 2001.

How reliable are the new numbers? The paper reports that "the absolute calibration is known to 2% in the shortwave (SW) and 1.5% in the longwave (LW) at the 95% confidence level."

This calibration uncertainty prompts the authors to state that "it is not surprising that satellite observations produce larger net TOA flux imbalances than expected". The next paragraph, however, does note that the adjustments made to the satellite data by Fasullo and Trenberth (2008) -- in attempt to reconcile the data with modeling -- were obviously too big. Well, those are my words, not theirs. The way the paper puts it is "Recently, Fasullo and Trenberth (2008) adjusted CERES SW and LW TOA fluxes to be consistent with observations of ocean and land heat storage (Willis et al., 2004; Huang, 2006) by uniformly increasing outgoing LW TOA flux by 1.5 Wm-2, and uniformly increasing albedo by ≈4% (relative to the original value). The adjustments are meant to account for uncertainties in angular models, scene identification, diurnal sampling, etc. We note, however, that the SW adjustment exceeds the global mean CERES SW TOA flux uncertainty determined in the present study by a factor of ~2."

The authors do not claim that the data invalidates estimates of the energy imbalance. Hansen's 0.85 +/-0.15 Wm-2 estimate is actually embraced by the paper, albeit in language that is more faith-based than anything else in the paper. Here's how Loeb et al put it in the body of the paper: "the 0.85 Wm-2 net flux imbalance believed to be real". The abstract refers not to belief, but to best estimate: "The 5-year global mean CERES net flux from the standard CERES product is 6.5 Wm-2, much larger than our best estimate of 0.85 Wm-2 based on observed ocean heat content data and model simulations." The difference might be partly due to the calibration error (which "accounts", the authors say, "for up to 4.2 Wm-2 of the 6.5 Wm-2 net TOA flux imbalance in the SRBAVG-GEO product"). It seems to me that the very language they use indicates an intent to avoid casting doubt on the Hansen estimate. They go on to quantify the error range associated with several other uncertainties and report "When all of these errors in solar irradiance, SW and LW TOA flux are combined, and the 0.85 ±0.15 Wm-2 of heat storage by the Earth-atmosphere is included (Hansen et al., 2005), the possible range of net TOA flux becomes -2.1 Wm-2 to 6.7 Wm-2, which bounds the 6.5 Wm-2 SRBAVG-GEO net TOA flux in Table 1." The summary section of the paper gives a slightly larger possible range: "Because of uncertainties in absolute calibration and the algorithms used to determine the Earth's radiation budget, satellite-based data products show a sizeable imbalance in the average global net radiation at the TOA, ranging from -3 Wm-2 to 7 Wm-2."

This paper reports on data from a 5-year period, which is less than the period considered in the 2002 Wielicki et al. paper. The shorter period does not lend itself to determining trends, but I respectfully note the lack of any discussion of the implications of the "accounting" practices (recommended by the authors) on the surprising trends reported in 2002 sticks out like a sore thumb. This kind of one-sided discussion is what I've come to call the "Trenberth fingerprint", and sure enough, the authors thank Dr. Trenberth for helpful discussion in the acknowledgements. From the IPCC WG1 AR4's treatment of the Wielicki et al. 2002 findings, it seems obvious to me that there is as dogged a determination to get rid of that trend as there was for getting rid of the Medieval Warm Period.

The paper includes an interesting discussion of recent total solar irradiance data, as follows: "According to recent measurements by the Total Irradiance Monitor (TIM) aboard the Solar Radiation and Climate Experiment (SORCE) satellite, the annual average solar irradiance at the TOA and 2σ uncertainty is 1361 ±0.8 Wm-2 (Kopp et al., 2005). This is approximately 4 Wm-2 lower than what is assumed in SRBAVG-GEO to determine net TOA flux, which is based on solar irradiance measurements from missions prior to SORCE. Averaged over the globe, the 4 Wm-2 difference between SORCE-TIM solar irradiance and the assumed SRBAVG-GEO value corresponds to +1 ±0.2 Wm-2 in net TOA flux. We assume the SORCE-TIM value is correct and the SRBAVG solar irradiance has bias of +1 Wm-2. The question of whether the solar irradiance is 1361 Wm-2 or is closer to 1365 Wm-2 is a topic of much recent debate within the solar radiation community. A Workshop in 2005 at the National Institute of Standards and Technology (NIST) partially explained the reasons for the discrepancies (Butler et al., 2008). Basedon intra-instrument cavity comparisons, the report notes that some of the instruments have underestimated their uncertainty (TIM was not one of them). It points out that part of the reason for the difference between TIM and the other instruments is associated with the optical design of the instruments. For example, most instruments place a view-limiting aperture near the front of the instrument and a precision aperture close to the cavity. Only TIM reverses this order by placing a narrow precision aperture at the front and a view-limiting aperture near the cavity. As a result, TIM minimizes the amount of scattered light in the instrument that can erroneously increase the signal. Another important factor is diffraction. Most instruments prior to TIM did not make a correction for light diffracted into the cavity. When a diffraction correction is applied to the three Active Cavity Radiometer Irradiance Monitors (ACRIMs), the solar irradiance is reduced by as much as 1.8 Wm-2. While these explanations do not account for the entire 4 Wm-2 difference in solar irradiance, they do suggest that measurements from several older instruments are too high, and that they get closer to TIM when the appropriate corrections are made. Another positive bias is associated with how the global average solar irradiance is calculated. It is common practice to assume a spherical Earth when averaging TOA insolation over the Earth's surface. This gives the well-known So/4 expression for mean solar irradiance, where So is the instantaneous solar irradiance at the TOA. When a more careful calculation is made by assuming the Earth is an oblate spheroid instead of a sphere, and the annual cycle in the Earth's declination angle and the Earth-sun distance are taken into account, the division factor becomes 4.0034 instead of 4. The spherical Earth assumption causes a +0.29 Wm-2 bias in net TOA flux. Similarly, assuming a spherical Earth in determining the global average SW and LW TOA fluxes (by using a latitude weighting in geocentric instead of geodedic coordinates) results in +0.18 Wm-2 and -0.05 Wm-2 biases, respectively."

The abstract is available here, with link to full paper.

Underview

The large variation -- first reported in a pair of Science articles in 2002 -- in top-of-atmosphere reflected solar (shortwave) and emitted thermal (longwave) was considered surprising by the authors (even without considering the apparent trend discovered) because none of the bigtime models could reproduce such significant variations. That the magnitude of the trend was so high (more Wm-2 of forcing in a decade than the entirety of estimated forcing from CO2 since industrial age began) was also a big deal. The IPCC AR4 handled the issue by saying the data was equivocal, and pretty much portrayed it as not worthy of much attention [note for posterity: If the IPCC applied the same criteria in their assessment of all the issues, their reports would surely not be so alarmist].

This latest paper seems intent on demonstrating that Hansen's energy imbalance estimate is not outside the bounds of uncertainty of the measurements. But the paper does this in a way that has significant implications that I think are even more problematic for the view they hold about the imbalance. If the actual values are indeed at the same bounding end of the uncertainty year-in and year-out, then the observed variation and trend values are maximized.

September 11, 2008

Examples of relatively comprehensive views on CO2-climate debate

I'd like to point folks to a pair of multidisciplinary "skeptic" reports that provide a good introduction to why the alarmist views are not shared by many scientists. The first report is called the ISPM -- the Independent Summary for Policymakers. Having seen how the alarmists used previous IPCC reports, a group of diligent dissidents started working on the ISPM at the point in the IPCC process that no further wide distribution of drafts would occur. One of the nice differences between ISPM and the IPCC's SPM is that real scientists were polled on how well the ISPM succeeded in being rigorous and comprehensive. The ISPM scored very highly. IPCC does not poll the folks who worked on the early stages to see how they consider the final product. The ISPM was released in February 2007 and is available as pdf via link on Ross McKitttrick's page describing the report here.

The second report is known as the NIPCC -- the Nongovernmental International Panel on Climate Change. Fred Singer edited this. It was released in March 2008. PDF is available here.

August 16, 2008

What is calamitology?

I first read it in an op ed a few years ago co-authored by a Harvard astrophysicist who was ridiculing the alarmist interpretation of climate data and whatnot. But I've come to learn that the term was coined decades ago. A 1964 article in Science reports that in 1952, a pair of geophysicists at the Office of Naval Research in Washington, DC were sorting research proposals, and "they concluded that the existing research categories were inadequate for the diversity of the proposals. Everything, it seems, was falling into miscelleneous piles. So, then and there, they decided to establish a miscelleneous society to accomodate diversity; AMSOC was thus born [American Miscelleneous Society], and in short order many of the outstanding figures of American science spoke proudly of their AMSOC affiliation, though it is clear that if AMSOC were any less of a society it would have been nonexistant. As an organization, its chief function seemed to be to revel in whimsy and in contributing its free-wheeling and witty ways with the ponderous motions of the standing professional societies. AMSOC delighted in its lack of membership rolls, bylaws, officers, publications, and formal meetings. Its only divisions, it noted, were in Etceterology, Phenomenology, Calamitology, Generology, and Triviology. It also maintained, it was pleased to point out, relations with the Committee for Cooperation with Visitors from Outer Space, as well as with the Society for Informing Animals of Their Taxonomic Positions..." [Source: D.S. Greenberg, "Mohole: The Project That Went Awry", Science, 143(3602):115-119, Jan. 10, 1964]

About calamitology.com

My name is Steve Schulin. I'm a candidate for Congress in Maryland's 4th district. I was born in 1954 and have been interested in energy and environment issues throughout my academic and professional years. I never had any desire to get involved in political party building or running for office. But I'm disgusted at the miserable failure of leadership represented by the candidates who emerged from the dominant parties this year. I support Alan Keyes' decision to run for President as an independent. You can find out more about Dr. Keyes and our new national political party at America's Independent Party. My own campaign website is md4steve.org.

Today's news items

April 18, 2009

Must-read from Monckton

His letter from UK to Reps. Markey and Barton: "...certain national and international executive agencies may have materially, serially, seriously, and successfully misled your Congress for several years about the imagined extent, anthropogenic component, and effects of 'global warming'."

April 14, 2009

* Australian geologist Ian Plimer has written a book about global climate, titled Heaven and Earth. It's being published today. A review in one of the Australian newspapers portrays the book as quite critical of the so-called consensus view. Here's a quote from the book: "The IPCC process is related to environmental activism, politics and opportunism. It is unrelated to science. Current zeal around human-induced climate change is comparable to the certainty professed by Creationists or religious fundamentalists." See the full review here.

October 7, 2008

* David Douglass and John Christy (2008), Limits on CO2 Climate Forcing from Recent Temperature Data of Earth Energy & Environment (accepted, August 2008)

The authors conclude that atmospheric temperature data does not show CO2 forcing signature. They note that " These conclusions are contrary to the IPCC [2007] statement: '[M]ost of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.'" Those who are interested in the differences between competing analyses of the data from satellite-borne MSU/AMSU will also appreciate the Appendix included in this paper comparing UAH and RSS products.

October 6, 2008

* ['Solar Weather Technique' forecaster lambastes CO2-alarmists]
Piers Corbyn has been making a living on long-range weather forecasting for the UK for many years. Recently, he's been applying his technique to other areas. His Weather Action website today includes a variety of extreme event forecasts for the coming month, and a humdinger of a critique of those who claim CO2 emissions are driving our climate: "CO2 has never driven, does not drive and never will drive weather or Climate. Global warming is over and it never was anything to do with CO2. CO2 is still rising but the world is now cooling and will continue to do so. Those who claim man's CO2 is driving weather or Climate must produce evidence. They cannot do so because there is no such evidence and they cannot even forecast anything. All they do is wait for extreme events and say that whatever happens is what they expected. Such drivel should not be allowed to pass yet shamefully many who style themselves as science correspondents and experts promote this nonsense. Global Warming is a deceitful political game. The UN IPCC must be called to account and integrity in science and politics must be restored."

September 26, 2008

* Chenoweth, M., and D. Divine (2008), A document-based 318-year record of tropical cyclones in the Lesser Antilles, 1690–2007, Geochem. Geophys. Geosyst., 9, Q08013, doi:10.1029/2008GC002066

Chenoweth and Divine say this new paper presents "the most comprehensive and longest document-based time series of tropical cyclone activity for any area of the world". The paper made Science magazine's "Editors' Choice: Highlights of the recent literature" this week. Newspaper accounts, ships' logbooks, meteorological journals, official colonial correspondence, and other document sources were used to create this new data set for the Atlantic and Caribbean region of the Lesser Antilles for the years 1690–2007. This region is along the main track of storms that eventually develop and hit the United States and Mexico. The authors identified 550 tropical storms and hurricanes passing through these islands, about half of which were not previously detected, including in more recent records. Overall, there seems to be no discernable trend in activity since 1690, though the time span 1968–1977 was probably the most inactive period since the islands were settled in the 1620s and 1630s. That last phraseology is straight from the abstract. Science chose to portray the 1968-77 period as follows: "the period from 1968 to 1977 had notably few storms". Why does Science choose to obfuscate just how notably few? Well, good luck getting an answer. I think Science is severely biased in favor of the calamitologists, and this is a soft-pedaling of findings that tend to contradict the alarmists. But I happily admit that Science highlights the paper, rather than ignoring it, so severe bias isn't equivalent to total blackout.

* [Colin Powell urges USA to take the lead on global warming]

He said America must be the world leader in the fight against global warming, as research, conservation and finding efficient fuel sources will help Americans be faithful stewards. He highlighted other matters requiring action including that the African-American community has a 50 percent high school drop-out rate.

September 13, 2008

* [Lomborg cedes anthropogenic warming, but hits NYT reporter's book as over-the-top]

The only thing in Thomas L. Friedman's new book -- Hot, Flat, and Crowded -- that Bjorn Lomborg admits to agreeing with is that keeping CO2 emissions stable at today's levels until 2050 would require the equivalent of building 13,000 new nuclear reactors around the world -- or roughly one new nuclear reactor every day for the next four decades. "Mr. Friedman is a smart guy, and he has interviewed a lot of interesting people" for the book. Lomborg wrote. "The problem is that they are essentially all on the same side of the issue. His sources are mostly climate campaigners, politicians who've made climate a big issue and businessmen who would gain a lot from regulation. Not surprisingly, they fundamentally agree on the size of the problem and its solutions. None of Mr. Friedman's interview subjects mentions that the global sea-level rise has remained steady since satellite measurements began, pointing toward an increase of one foot by the end of the century. Over the past two years, in fact, sea levels have probably slightly dropped." Lomborg's name been associated with skepticism of alarmist claims about CO2 and climate. But in this Wall Street Journal piece, Lomborg again distances himself from the word that sold a multitude of his books. He is as shamefully ignorant as the alarmists in his caricaturing of real skeptics: "Let's be clear", he says. "Global warming is real and man-made... Denying climate science is foolish." What the skeptics deny, Mr. Lomborg, are notions expressed by pretentious yahoos and others that the science warrants jumping to the alarmist conclusions so often portrayed as 'the consensus'.

September 12, 2008

* [federal energy funding - proposal to triple]

MIT President Susan Hockfield has called for Congress to lead in priming the energy reserach pump. Pharmaceutical companies invest 18 percent of revenue in R&D. Semiconductor firms invest 16 percent. Energy companies invest less than one-quarter of 1 percent. With this pattern of investment, we cannot expect an energy technology revolution. Federal funding for energy research has dwindled to irrelevance, she says. In 1980, 10 percent of federal research dollars went to energy. Today, the share is 2 percent. Research investment by U.S. energy companies has mirrored this drop. In 2004, it stood at $1.2 billion in today's dollars. This might suit a cost-efficient, technologically mature, fossil-fuel-based energy sector, but it is insufficient for any industry that depends on innovation. We stand on the verge of a global energy technology revolution, she says, and asks "Will America lead it and reap the rewards? Or will we surrender that advantage to other countries with clearer vision?"

* [US presidential election]

In an interview with a Fairbanks newspaper within the last year, Palin said: "I'm not an Al Gore, doom-and-gloom environmentalist blaming the changes in our climate on human activity." However, she told Charlie Gibson of ABC News Thursday that "man's activities certainly can be contributing to the issue of global warming, climate change. ... Regardless, though, of the reason for climate change, whether it's entirely, wholly caused by man's activities or is part of the cyclical nature of our planet — the warming and the cooling trends — regardless of that, John McCain and I agree that we gotta do something about it." Palin, 44, has been Alaska's governor for less than two years and before that was a small-town mayor. Asked whether those were sufficient credentials, Palin said: "It is about reform of government and it's about putting government back on the side of the people, and that has much to do with foreign policy and national security issues." She said she brings expertise in making the country energy independent as a former chairman of the Alaska Oil and Gas Conservation Commission.

September 9, 2008

* [global cooling forecast]

The Old Farmer's Almanac hit the newsstands Tuesday saying a study of solar activity and corresponding records on ocean temperatures and climate point to a cooler, not warmer, climate, for perhaps the next half century. "We at the Almanac are among those who believe that sunspot cycles and their effects on oceans correlate with climate changes," writes meteorologist and climatologist Joseph D'Aleo. "Studying these and other factor suggests that cold, not warm, climate may be our future." It remains to be seen, said Editor-in-Chief Jud Hale, whether the human impact on global temperatures will cancel out or override any cooling trend. "We say that if human beings were not contributing to global warming, it would become real cold in the next 50 years," Hale said.

* [cool-colored roofs save energy]

"White roofs can cut a building's energy use by 20 percent and save consumers money," says California Energy Commissioner Art Rosenfeld. "The potential energy savings in the U.S. is in excess of $1 billion annually. In a study to be published in the scientific journal "Climate Change," Rosenfeld and Lawrence Berkeley National Laboratory scientists Hashem Akbari and Surabi Menon estimate that replacing nonreflective, dark roofing materials with white ones on an average house with 1,000 square feet of roof would result in an equivalent CO2 offset of 10 metric tons annually. The scientists propose an international campaign to organize 40 of the world's largest cities in tropical and temperate zones to develop programs to require white roofs and "cool pavements" when roofs are initially constructed and pavements installed. The projected estimate for worldwide CO2 emissions in 2025 is 37 billion metric tons; a proposed global CO2 offset would be 44 billion metric tons, valued at $1,100 billion, and enough to offset more than one year of the total global CO2 emissions, they say. Since 2005, commercial buildings with flat roofs in California have been required to have white roofs. Residential sloped roofs are also becoming more efficient. Beginning next year, new residential roofs and retrofit constructions in California will be required to have "cool-colored" roofs which reflect a higher fraction of the sun's rays than current roofing materials of the same color.