Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


Mercury rising: Greater L.A. to heat up an average 4 to 5 degrees by mid-century

Posted on 25 June 2012 by dana1981


Before and after: Current and projected temperature extremes in the L.A. area.

A groundbreaking new study led by UCLA climate expert Alex Hall shows that climate change will cause temperatures in the Los Angeles region to rise by an average of 4 to 5 degrees Fahrenheit by the middle of this century, tripling the number of extremely hot days in the downtown area and quadrupling the number in the valleys and at high elevations.
Released today, "Mid-Century Warming in the Los Angeles Region" is the first study to provide specific climate-change predictions for the greater Los Angeles area, with unique predictions down to the neighborhood level. The report, the most sophisticated regional climate study ever developed, was produced by UCLA with funding and support from the city of Los Angeles (news release), in partnership with the Los Angeles Regional Collaborative for Climate Action and Sustainability (LARC). It is available online at
"The changes our region will face are significant, and we will have to adapt," said Hall, an associate professor in UCLA's Department of Atmospheric and Oceanic Sciences who is also a lead author on the Intergovernmental Panel on Climate Change reports, which, among other things, assess global climate-change simulations for the United Nations.
"Every season of the year in every part of the county will be warmer," Hall said. "This study lays a foundation for the region to confront climate change. Now that we have real numbers, we can talk about adaptation."
The LARC's unprecedented coalition of cities, universities, businesses, non-profits and other agencies made the study possible. Mayor Antonio Villaraigosa and the city of Los Angeles led the way, obtaining a $613,774 grant from the U.S. Department of Energy to study and share climate research and committing $484,166 to commission UCLA's climate-change study. Though scientists knew to expect warming, this is the first time policymakers in the Los Angeles area have precise information on which to base their plans.
"UCLA's model shows projected climate changes down to the neighborhood level, allowing us to apply the rigor of science to long-term planning for our city and our entire region," Villaraigosa said. "With good data driving good policies, we can craft innovative solutions that will preserve our environment and enhance the quality of life for the next generation of Angelenos."  
Facts and figures from the study
The study looked at the years 2041–60 to predict the average temperature change by mid-century. The data covers all of Los Angeles County and 30 to 60 miles beyond, including all of Orange County and parts of Ventura, San Bernardino and Riverside counties, and reaching as far as Palm Springs, Bakersfield and Santa Barbara. The study overlaid this entire area with a grid of squares 1.2 miles across and provided unique temperature predictions for each square. This is in contrast to global climate models, which normally use grids 60 to 120 miles across — big enough to include areas as different as Long Beach and Lancaster.
According to the study, coastal areas like Santa Monica and Long Beach are likely to warm an average of 3 to 4 degrees. Dense urban areas like downtown Los Angeles and the San Fernando and San Gabriel valleys will warm an average of 4 degrees, and mountain and desert regions like Palm Springs and Lancaster will warm 4 to 5 degrees.
Some of the smallest changes predicted, yet still nearing a 4-degree increase, are in Oxnard (3.68 degrees), Venice (3.70), Santa Barbara (3.73), Santa Monica (3.74), San Pedro (3.78), Torrance (3.80), Long Beach (3.82) and Santa Ana (3.85). Among the highest predicted increases are Wrightwood (5.37), Big Bear Lake (5.23), Palm Springs (5.15), Palmdale (4.92), Lancaster (4.87), Bakersfield (4.48) and Santa Clarita (4.44). Table 2 in the study calls out 27 distinct locations, such as downtown Los Angeles (3.92), San Fernando (4.19), Woodland Hills (4.26), Eagle Rock (3.98), Pasadena (4.05), Pomona (4.09), Glendale (3.99) and Riverside (4.23).
These figures are only annual averages, and the day-to-day increase in temperatures will vary, said Hall, who is a member of UCLA's Institute of the Environment and Sustainability (IoES) and director of the institute's Center for Climate Change Solutions. Southern Californians should expect slightly warmer winters and springs but much warmer summers and falls, with more frequent heat waves. Temperatures now seen only on the seven hottest days of the year in each region will occur two to six times as often. The number of days when the temperature will climb above 95 degrees will increase two to four times, depending on the location. Those days will roughly double on the coast, triple in downtown Los Angeles and Pasadena, and quadruple in Woodland Hills. In Palm Springs, the number of extremely hot days will increase from an annual average of 75 to roughly 120.
"Places like Lancaster and Palm Springs are already pretty hot areas, and when you tack on warming of 5 to 6 degrees, that's a pretty noticeable difference," Hall said. "If humans are noticing it, so are plants, animals and ecosystems. These places will be qualitatively different than they are now."
The most sophisticated regional climate study ever developed
The type of climate modeling used in the study is done almost exclusively at the national or international level, said Paul Bunje, the managing director of the LARC, which is based at UCLA's Institute of the Environment and Sustainability. Other cities and states have localized global climate models — but usually by localizing only one model. Hall's team needed months of computer time to downscale 22 global climate models, each with slightly different assumptions about how to predict climate change or factors like future greenhouse gas emissions.
Hall's team included UCLA postdoctoral students Fengpeng Sun and Daniel Walton and graduate student Mark Nakamura. Once they recalculated the almost two dozen global models at the local level, the team analyzed the results and integrated them into an ensemble projection to create the forecast for the entire region.
"This is the best, most sophisticated climate science ever done for a city," said Bunje, who is also the executive director of UCLA's IoES Center for Climate Change Solutions.
"L.A. is one of the first cities to get its act together, from the scientists all the way up to the mayor," Bunje said. "Nobody knew precisely how to adapt to climate change because no one had the data — until now. These are shocking numbers, and we will have to adapt."
Cutting emissions will reduce but not eliminate warming
Cutting greenhouse gas emissions could reduce the impact on Los Angeles, Hall said. However, even if the world has unanticipated — and perhaps unrealistic — success in drastically reducing greenhouse gas emissions, the greater Los Angeles area will still warm to about 70 percent of the currently predicted levels, the study found.
"We looked not only at a business-as-usual scenario where greenhouse gas emissions continue but also at a scenario where emissions are curtailed," Hall said. "Even if we drastically cut pollution worldwide, there will still be quite a bit of warming in Los Angeles. I was a little taken aback by how much warming remains, no matter how aggressively we cut back. It was sobering."
"Mid-Century Warming in the Los Angeles Region" is the first of five planned studies Hall will conduct for the city and the LARC about how climate change will affect the Southland. Hall's team plans to develop similarly comprehensive models for local rainfall, Santa Ana wind patterns, coastal fog (including June gloom), and soil moisture, run-off and evaporation. Preliminary results already show that Santa Ana winds and June gloom will react to climate change, Hall said.
Global warming is local warming
"I think for many people, climate change still feels like a nebulous, abstract, potential future change, and this makes it more real," Hall said. "It's eye-opening to see how much it will warm where you live. This data lays a foundation for really confronting this issue, and I'm very optimistic that we can confront and adapt to a changing climate."
The complete study, "Mid-Century Warming in the Los Angeles Region," along with interactive maps and ways to get involved, can be accessed online at
The Los Angeles Regional Collaborative for Climate Action and Sustainability is a regional network developing the science and strategies to address climate change. The LARC brings together leadership from government, the business community, academia, labor, and environmental and community groups to encourage greater coordination and cooperation at the local and regional levels. The goals are to share information, foster partnerships, develop systemwide strategies to address climate change, and promote a green economy. The collaborative is housed at the UCLA Institute of the Environment and Sustainability and is governed by the LARC Steering Committee.
The UCLA Institute of the Environment and Sustainability is an educational and research institute that unites disciplines: physical, life and social sciences; business and economics; public policy and urban planning; engineering and technology; and medicine and public health. IoES includes multiple cross-disciplinary research centers, and its environmental science undergraduate degree program is one of the fastest growing majors at UCLA. IoES advises businesses and policymakers on sustainability and the environment and informs and encourages community discussion about critical environmental issues.
For more news, visit the UCLA Newsroom and follow us on Twitter.

0 0

Printable Version  |  Link to this page


Comments 1 to 15:

  1. They are lucky, The U.S.A. being one of the places in the world that will be least affected by climate change. Some poor sods stand little or no chance of adapting to it other than by burying their dead, of course. It would be nice if, when planning their adaptation strategies, these American experts could offer advice to their less fortunate fellow humans who live in parts of the world that will be most affected by it. Especially seeing as these people often have neither the expertise nor the time, what with subsistence farming to cope with, and Aids and water shortages and and and.
    0 0
  2. Los Angeles is one of the largest urban heat islands in the U.S. Is Alex Hall's predicted temperature increase for the L.A. region NET of UHI temp increases arising from projected population growth? What did Hall use as the projected L.A. temperature increase due to population growth through mid-century?
    0 0
  3. The heat around the LA area depends almost entirely on offshore versus onshore winds. The global model cannot predict that pattern so they used downscaling. Reading through the study here I see in the appendix that the offshore vs onshore parameters (alpha and beta) are determined from a minimizing the error between the global and regional models. Thus, alpha and beta are a function of three parameters from the global model (lapse rate, along with warming and ocean to desert contrast). The most obvious flaw is that the onshore vs offshore regime will depend on the larger climate pattern. For example the past winter's La Nina created more offshore winds. It does not appear that there is any connection from such climate regimes in the global model to the local model as they state in the paper the connections are mostly through temperature, contrast and lapse rate. Here's an alternative scenario: [LINK]
    0 0
    Moderator Response: [RH] Shortened link that was breaking page formatting.
  4. daisym: Well, UHI is usually a function of the logarithm of population (Oke, 1967), so the effect tapers off as growth continues, and it's usually caused by changing land use (pavement replacing natural surfaces, heat retention in artificial structures, etc.). How much more growth can the LA basin handle, and how much of it is still left in a natural state, to pave over?
    0 0
  5. Daisym This peer reviewed paper shows little effect from UHI on urban temperatures in the USA. Fake skeptics claim UHI causes everything. Can you provide a peer reviewed study that suggests UHI affects the result of the opening post or are you just hand waving? Hand waving arguments can be dismissed with a hand wave. In any case, UHI changes are well known to have little effect on decade level temperature changes.
    0 0
  6. Michael, you seem to have misread both Daisym's comment and your own reference. Daisym didn't suggest that the UHI has the effect to bias temperature anomaly reconstructions. And your reference only denies that the UHI causes any significant such bias. That's in part because "urban meteorological observations are more likely to be made within park cool islands than industrial regions"
    0 0
  7. Pierre: It appears to me that Daisym is challenging the OP, claiming that UHI has not been properly taken into effect. Perhaps I am incorrect, Daisym could tell me if that is the case. The link I provided was the first of many that show UHI has a small effect on these types of measurement. My reference "denies" nothing. They provide data that show the UHI effect is small. I could have cited Watts paper where they show "improperly" located weather stations have no effect on temperature trends. In general, UHI is a non effect that deniers cite to confuse people. AGW fake skeptics often raise tone questions of this type to suggest data issues that do not exist. What is your point?
    0 0
  8. Michael, I only pointed out that your reference 'denies that...' in the sense of 'affirming the falsity of...' in its conclusion. That was an innocent use of the word "denies". The paper concludes that the UHI doesn't introduces significant bias in temperatures reconstructions. But that conclusion doesn't speak at all to Daisym's question. Daisym only seemed to be inquiring if the UHI effect (that your reference acknowledges to be real and significant albeit not a source of measurement bias) is accounted for in the models predictions. This is a good question, it seems to me, since the models are so finely gridded so as to geographically discriminate some industrial from residential or rural areas.
    0 0
  9. Pierre: Please provide a reference that shows the models are finely enough gridded to discern between industrial and residential areas. It seems to me that if I misinterpreted Daisym's question it is up to her to clarify the misunderstanding. You might be the one misinterpreting her question. While UHI is a real effect, it is very small. Numerous studies, including BEST, showed that it makes no difference to temperature trends whether you correct for UHI or not. Since the authors and reviewers of the paper are professionals it should be presumed that they considered any important effects unless data is provided to show that they did not. No data has been provided to show anything important was left out. Asking a question does not show that the authors made a mistake. If you think it is a good question, read the paper and see what they say.
    0 0
  10. Pierre; I re-read the abstract of the paper that I linked above. You seem to have misinterpreted their conclusion. Your quote above is incomplete and gives an incorrect summary of the abstract. It should read: "Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures. It is postulated that this is due to micro- and local-scale impacts dominating over the mesoscale urban heat island. Industrial sections of towns may well be significantly warmer than rural sites, but urban meteorological observations are more likely to be made within park cool islands than industrial regions." My emphasis. I have provided data that shows UHI is not important to the OP. Please provide data to support your claim that UHI is important. As I said above "In general, UHI is a non effect that deniers cite to confuse people. AGW fake skeptics often raise tone questions of this type to suggest data issues that do not exist. What is your point?"
    0 0
  11. Michael, the part that you put in bold is a point that have explicitly granted twice. To suggest that this point didn't seem in dispute was the very reason I replied to you in the first place. Daisym was inquiring about model predictions, not past reconstructions from station measurements. This is a different topic. You need not lash at someone just because the "UHI" acronym figures in her post. You now ask me for a reference that shows the models are finely gridded enough to discern between industrial and residential areas. That's in the OP. "The study overlaid this entire area with a grid of squares 1.2 miles across and provided unique temperature predictions for each square. This is in contrast to global climate models, which normally use grids 60 to 120 miles across." This seems finely gridded enough to make Daisym's question at least relevant.
    0 0
  12. Pierre: It is good that we agree that UHI has not caused significant temperature increases in the past. You claim future temperature might be affected by UHI when it has been shown that past temperature have not. While it is always possible for the future to be different than the past, it does not seem to me to be a legitimate question. AGW fake skeptics repeatedly ask the same questions to be constantly addressed again and again. This is not how science works. If we show something was true in the past you need to provide data to support your contention that in the future those properties will change. The model described in the OP is sufficiently detailed that it is unreasonable to suggest that experienced scientists did not consider UHI without providing data to support such an extraordinary claim. You have not provided any data to support your position, merely hand waving. Hand waving claims can be dismissed with a hand wave. This discussion has deteriorated. If you do not provide data to support your claims I will no longer respond.
    0 0
  13. Michael: "Industrial sections of towns may well be significantly warmer than rural sites, but urban meteorological observations are more likely to be made within park cool islands than industrial regions." The question about the future bears no relationship to the strawman claim about the past you keep beating up. Your reference acknowledges the UHI effect. It's just that station siting doesn't introduce any significant bias in the reconstructions of historical temperature anomalies. That's because (1) the sampling isn't biased, and (2) the reconstructions aren't spatially fine-grained. This is as should be. They're meant to pick up climate signals. But the question about the future isn't a question about climate signals, but a question about causes of high frequency spatial variation. They're two separate issues that you keep conflating. Look at the map in the OP and how greatly both current observations and modeled predictions vary over areas just a few miles apart. Are you suggesting that only variations in natural geography can account for it and urban geography likely plays no significant role? I can't see why the contrary suggestion (merely a question, actually) would be extraordinary and require extraordinary evidence.
    0 0
  14. I think this answers Daisym's query: "It is plausible that the unique surface thermal properties of urban areas (e.g. heat capacity, emissivity, conductivity) could also affect the warming there. While these properties are included in the Noah land surface model, there is little evidence that they result in a differentiated urban effect, because the warming in the urbanized coastal zone is so similar to that over the coastal ocean." Hall et al. p.11
    0 0
  15. Can I ask that headlines referring to temps in ºF and so departing from the international scientific convention of ºC make this clear in the headline itself?
    0 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us