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Published: Saturday 14 September, 2013

shop of shoes shop of shoes Are the IPCC climate change models overestimating sensitivity to carbon dioxide

A recent report in The Register suggests that we might be currently overestimating the degree to which the world will warm with increasing carbon dioxide.

Climate sensitivity is, crudely, the slope of the relationship between CO2 levels and average world temperature. It is usually expressed as the number of degrees Celsius that will result from a doubling of CO2 concentration. If everything else were equal and the only effect was driven by the properties of CO2 then the sensitivity would be about 1C. But many o shop of shoes ther factors also change in the real atmosphere, for example the concentration of water vapour, also a powerful greenhouse gas. So scientists have to find ways to estimate those other effects based on models or observations of the real, very complicated, atmosphere. The current consensus seems to centre around 3C.

When the researchers instead calculate a probability interval of what will occur, including observations and data up to 2010, they determine with 90% probability that global warming from a doubling of CO2 concentration would lie between 1.2C and 2.9C.

This maximum of 2.9C global warming is substantially lower than many previous calculations have estimated. Thus, when the researchers factor in the observations of temperature trends from 2000 to 2010, they significantly reduce the probability of our experiencing the most dramatic climate change forecast up to now.

Berntsen and his colleagues results derive in large part from taking account of the way that global temperatures have remained flat for the last fourteen years or thereabouts, instead of climbing as they ought to have done with increased carbon levels.

The Earths mean temperature rose sharply during the 1990s. This may have caused us to overestimate climate sensitivity, explains the prof. That claim fails Hanlon Razor. If the scientific consensus is right, any answer will either be crackpot or merely repeating the scientific consensus, neither of which is helpful. If the scientific consensus is wrong, the answer saying so will be judged to be wrong, which is also unhelpful. Oddthinking Feb 4 at 0:20

When the researchers at CICERO and the Norwegian Computing Center applied their model and statistics to analyse temperature readings from the air and ocean for the period ending in 2000, they found that climate sensitivity to a doubling of atmospheric CO2 concentration will most likely be 3.7 which is somewhat higher than the IPCC prognosis. But the researchers were surprised when they entered temperatures and other data from the decade 20002010 into the model; climate sensitivity was greatly reduced to a mere 1.9 10 years of data causes that much of a change to the result obtained from 250 years of data, its quite possible that their method is overweighting the most recent data. Its giving too much weight to a small number of recent years. Because the number of years is small, weather noise will dominate climate trends. Its worth noting at this point that some of the Cicero work behind this press release was unpublished at the time of the press release, and none of it has yet been confirmed by other studies.

Are we OK if forcing is, say, only 1 shop of shoes rather than 3 because even in that incredibly optimistic scenario which is not supported by the vast majority of empirical data and studies, were on course to raise CO2e from preindustrial levels of 280ppm to 1000ppm, which would lead to a raising of temperature of 34 which puts us into very dangerous territory.

Is it a safe bet to assume that sensitivity is much less?

No, its an insane gamble. And thats because the stakes are so high this is an asymmetric bet. Lets take an extremely optimistic case, one that is so optimistic that it defies the known science, that theres only a 5% chance that forcing is 3 and a 95% chance that forcing is 1 The cost of decarbonising the economy is uncertain it may be a net positive, or around 1% of GDP, and almost certainly below 5.5% of GDP. So, even in this extreme case where the vast bulk of climate science is wrong, the bet offered is at 95%:5%; the stake is human civilisation, and the potential value of a win is 1% to 5.5% of global GDP. Thats not a sane oneoff bet, its an insane gamble. If we were going to average it out over tens of thousands of cases, then statistics would be on our side. But this is a oneshot gamble, the odds are for a high forcing, and the stakes are way way in favour of decarbonisation.

Has there been a lack of warming over the last 14 years?

No, not unless the laws of physics have changed. And weve got no reason to believe they have. We know the sun has continued to irradiate the Earth, at the levels it has for many years. And we know that the Earths insulation, from greenhouse gases, has increased we know that from huge amounts of empirical observation. So we know that the global heat content has continued to rise that much is basic thermodynamics. A lot of heat gets stored in oceans; that means that it doesnt show up in surface temperatures, until we get one of those periodic releases of heat from oceans, which then boost global surface temperatures thereafter.

The FUD meme that has confused some nonscientists, that there has been a lack of warming over the last 14 years, has come about because there is no clear trend in surface temperatures over the last 14 years. Now, no clear trend is not the same as a flat horizontal trend, any more than its the same as a rising trend or a falling trend. Its no clear trend. No clear trend doesnt mean you get to pick and choose the trend that suits your fancy; it mea shop of shoes ns that theres insufficient evidence for what the trend is, in that particular dataset. That shouldnt be surprising: the surface temperatures of a small number of years are more likely to indicate the noise of weather, rather than trends in climate. Trends in climate tend to show up at the scale of 30 years or so, and over that timescale, the warming trend is unambiguous:

Climate sensitivity to carbon dioxide was based on the concept that CO2 was the cause of temperature rise during the previous 400,000 years, the Paleo period This is clearly not the case. In the Paleo period increased solar insolation was the cause of both CO2 and temperature rise. In the present period it is heat alone that is the cause. The fact that temperature tracks CO2 is because combustion of fossil fuels cause both the CO2 and temperature to rise. If nuclear power replaced fossil fuels temperatures would continue to rise while CO2 would begin to fall. Nuclear power emits twice the total heat as its electrical output. Focus on heat not CO2. shop of shoes