søndag 13. mai 2018

MYTH# 17 MODELS ARE NOT ACCURATE



Part of the problem here stems from people either misunderstanding or deliberately misrepresenting how predictive models work. Many people have the unrealistic expectation that the observed data need to be a near perfect match for the prediction line, but that’s not actually how things work. 


Some are still "under the mistaken impression that concern about global warming is based on climate models, which in reality play little role in our understanding -- our understanding is based mainly on how the Earth responded to changes of boundary conditions in the past and on how it is responding to on-going changes."
- Dr. James Hansen
 
 
There is an excellent description of climate models evaluation in the following IPCC report:
Page 600-601 that address how reliable current models are. The last paragraph states:
"In summary, confidence in models comes from their physical basis, and their skill in representing observed climate and past climate changes. Models have proven to be extremely important tools for simulating and understanding climate, and there is considerable confidence that they are able to provide credible quantitative estimates of future climate change, particularly at larger scales. Models continue to have significant limitations, such as in their representation of clouds, which lead to uncer- tainties in the magnitude and timing, as well as regional details, of predicted climate change. Nevertheless, over several decades of model development, they have consistently provided a robust and unambiguous picture of significant climate warming in re-sponse to increasing greenhouse gases."
 Q&A: How do climate models work?
https://www.carbonbrief.org/qa-how-do-climate-models-work
La oss se nærmere på hva forskerne har spådd/modellert og hvordan dette stemte med hva vi vet i dag. 


En grundig gjennomgang av klimamodellene viser oss at de har vært veldig nøyaktige og har truffet særs godt.   
" the close match between projected and observed warming since 1970 suggests that estimates of future warming may prove similarly accurate."!  
Comparing models and observations. 
USAs mest kjente prognosestatistiker, Nate Silver, viet et kapittel til samme spørsmål i sin bok "The Signal and the Noise: The Art and Science of Prediction". Her sammenlignet han prognosetreffsikkerheten fra tidlige klimamodeller med treffsikkerheten andre fag som forsøker å beregne fremtiden (makroøkonomi, seismologi, valgforskning, meteorologi, sportsresultater osv.) Klimamodellene kom bra ut av det. Sceptical Science har mer
"when correcting the model projections to account for the actual greenhouse gasemissions and forcing changes, we see that their temperature projections have been very accurate.[...] we don't even need climate models to realize that we're in for a lot of global warming this century." 

Robust comparison of climate models with observations using blended land air and ocean sea surface temperatures

Here are some actual predictions from Global Climate Models all of which have proven correct:


Here are some actual predictions from Global Climate Models all of which have proven correct:

1.That the globe would warm, and about how fast, and about how much.

2. That the troposphere would warm and the stratosphere would cool.

3. That nighttime temperatures would increase more than daytime temperatures.

4. That winter temperatures would increase more than summer temperatures.

5.Polar amplification (greater temperature increase as you move toward the poles).

6. That the Arctic would warm faster than the Antarctic.

7.The magnitude (0.3 K) and duration (two years) of the cooling from the Mt. Pinatubo eruption.

8.They made a retrodiction for Last Glacial Maximum sea surface temperatures which was inconsistent with the paleo evidence, and better paleo evidence showed the models were right.

9.They predicted a trend significantly different and differently signed from UAH satellite temperatures, and then a bug was found in the satellite data.

10.The amount of water vapor feedback due to ENSO.

11. The response of southern ocean winds to the ozone hole.

12.The expansion of the Hadley cells.

13.The poleward movement of storm tracks.

14.The rising of the tropopause and the effective radiating altitude.

15.The clear sky super greenhouse effect from increased water vapor in the tropics.

16.The near constancy of relative humidity on global average.

17.The expanded range of hurricanes and cyclones--a year before Cyclone Catarina showed up off the coast of Brazil, something which had never happened before.

The First Climate Model Turns 50, And Predicted Global Warming Almost Perfectly 

Modeling the Earth's climate is one of the most daunting, complicated tasks out there. If only we were more like the Moon, things would be easy. The Moon has no atmosphere, no oceans, no icecaps, no seasons, and no complicated flora and fauna to get in the way of simple radiative physics. No wonder it's so challenging to model! In fact, if you google "climate models wrong", eight of the first ten results showcase failure. But headlines are never as reliable as going to the scientific source itself, and the ultimate source, in this case, is the first accurate climate model ever: by Syukuro Manabe and Richard T. Wetherald. 50 years after their groundbreaking 1967 paper, the science can be robustly evaluated, and they got almost everything exactly right.
A study, out Wednesday in the journal Science Advances, joins a growing body of literature that suggests the models are on track after all. And while that may be worrisome for the planet, it’s good news for the scientists working to understand its future. Climate models are even more accurate than you thought The difference between modeled and observed global surface temperature changes is 38% smaller than previously thought. Global climate models aren’t given nearly enough credit for their accurate global temperature change projections. As the 2014 IPCC report showed, observed global surface temperature changes have been within the range of climate model simulations. 
Now a new study shows that the models were even more accurate than previously thought. In previous evaluations like the one done by the IPCC, climate model simulations of global surface air temperature were compared to global surface temperature observational records like HadCRUT4. However, over the oceans, HadCRUT4 uses sea surface temperatures rather than air temperatures.



James Hansen wishes he wasn't so right about global warming
https://abcnews.go.com/Technology/wireStory/james-hansen-wishes-global-warming-55969021

Models successfully reproduce temperatures since 1900 globally, by land, in the air and the ocean. CMIP5.
Klimaforsker Gavin Schmidt oppklarer

Sammenligner vi IPPC sine modeller med kjente klimaskeptikeres modeller ser vi at IPPC treffer ganske godt også med sine tidligste modeller, mens klimaskeptikerne bommer fælt. Her ser vi og hvordan klimaskeptikere misbruker IPPC sine data for å skape en myte om at IPPC har overdrevet sine temperaturframskrivninger.  
 
Ny forskning feier all tvil til side:  
Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends. "Trends starting in 1997 or 1998 are particularly biased with respect to the global trend. The issue is exacerbated by the strong El Niño event of 1997–1998, which also tends to suppress trends starting during those years."
The existence of bias in recent global mean temperature estimates has been confirmed by multiple means. This bias leads to an underestimation of recent temperature trends. The evidence is as follows. Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends. Kevin Cowtan, Robert G. Way (2014)
The new dataset shows substantially increased global-scale warming relative to the previous version of the dataset, particularly after 1998. The new dataset shows more warming than most other midtropospheric data records constructed from the same set of satellites. It is also shown that the new dataset is consistent with long-term changes in total column water vapor over the tropical oceans, lending support to its long-term accuracy.
Sensitivity of Satellite-Derived Tropospheric Temperature Trends to the Diurnal Cycle Adjustment Press Release: 2016 Tropospheric Temperatures. A new press release from Dr. Carl Mears using the Temperature Total Troposphere (TTT) dataset shows that 2016 is the warmest year since the satellite record began in 1979. The previous record, set during the last major El Niño in 1998, was broken by 0.31 degrees Fahrenheit.
A new paper just published in the Journal of Climate is a stunning setback for the darling of cherry-picking for contrarian scientists and elected officials. Let’s walk though this so we appreciate the impact.
In recent years, some scientists have suggested that our climate models may actually be predicting too much future warming, and that climate change will be less severe than the projections suggest. But new research is helping lay these suspicions to rest
What the scientists knew in 1982:

OVERDRIVER FORSKERNE OG SPÅR DE DOMMEDAGSSCENARIER?

En helt ny studie publisert i journalen Climate Change oppklarer.
Study Reviews 1,154 Climate Science Results, Finds No Evidence of Publication Bias
In our research, published in the journal Climatic Change, we analysed more than 1,100 published results from the field of climate change science and found no evidence of under-reporting or missing results – even results that were not statistically significant or showing no positive effects were reported.[...] In scientific terms, we reject the accusation made by climate change skeptics and can confirm that there is no publication bias in climate change research.  
Også FNs Klimapanel sine modeller fremskrivninger har blitt undersøkt:
Claims that the IPCC is alarmist are not supported by evidence, and there are clear indications that the opposite may be the case. "Numerous papers have documented how IPCC predictions are more likely to underestimate the climate response."
Checking 20 years worth of projections shows that the Intergovernmental Panel on Climate Change has consistently underestimated the pace and impacts of global warming. Her er studien som bekrefter dette: 
Climate scientists are not alarmists but have underestimated recent climate changes. ► We identify a directional bias toward erring on the side of least drama (ESLD). ► ESLD is an internal pressure arising from norms of objectivity, restraint, etc. ► ESLD may cause scientists to underpredict or downplay future climate changes. 

On the latest IPPC report:

"it is the report’s summary for policymakers that is causing concern. This is the document politicians will use as a key climate guide when making changes to legislation. Reviewers of earlier drafts say it is being altered to make the dangers of climate change seem less alarming. As a result, they say,, policymakers could seriously underestimate the risks of global warming. Cuts made to the final draft of the summary include:
 Any mention that temperature rises of above 1.5C could lead to increased migrations and conflict;
 All discussion of the danger of the Gulf Stream being disrupted by cold water flowing from the Arctic where more and more sea-ice is melting;
 Warnings about the dangers that 1.5–2C temperature rises could trigger irreversible loss of the Greenland ice sheet and raise sea levels by 1–2 metres over the next two centuries.
Other cuts from the summary include the sentence: “Poverty and disadvantage have increased with recent warming (about 1C) and are expected to increase in many populations as average global temperatures increase from 1C to 1.5C and beyond.”
MEDIENE HAR EN TENDENS TIL Å OVERDRIVE.
Mens klimaforskere advarer om økonomi, trygghet og mat, tegner gjerne mediene et dystrere eller mer sensasjonelt bilde. Klimafornektere liker å pushe en myte om at klimavitenskapen har spådd et "hollywood doom and gloom scenario" og når dette ikke kommer, ja da har de tatt feil igjen. men, som vi har sett, klimaforskernes modeller og "spådommer" er i ganske god kontakt med virkeligheten. 
Analysis: How well have climate models projected global warming?
Conclusion
Climate models published since 1973 have generally been quite skillful in projecting future warming. While some were too low and some too high, they all show outcomes reasonably close to what has actually occurred, especially when discrepancies between predicted and actual CO2 concentrations and other climate forcings are taken into account.
 

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