> In message <NDBBKPODIHENIECLLPBIKEFJCBAA.kmack at dimensional.com>, Kenneth
> Mack <kmack at dimensional.com> writes
> >It is not faith that tells me that increased levels of GHGs can
> >trap more energy, it is physics. If it is NOT trapping more energy then
> >there needs to be a mechanism to explain it.
>
> What's at issue is whether GHG emissions are responsible for global
> warming. To show that you have to show more than that it could be the
> reason, but also that it is. There is a quantitative question here.
>
> >There may well be a mechanism
> >to explain it, what is it? And if so, why the warmer temperatures?
>
> As is well known climate change predates human industry by about as long
> as there has been a climate.
>
The earth's climate has certainly changed through time. There is no doubt about it. But those changes can be explained by understanding the earth's orbital parameters, and the system of energy distribution. The earth has warmed and cooled over the last few million years in synchronicity with the earth's orbital parameters (the tilt of the earth's axis, the precession of the axis, and the orbital obliquity.) These parameters, known as Milankovitch cycles, dictate the insolation (amount of solar energy received in a location.) Glacial and inter-glacial time periods are driven by this cyclic insolation change. The insolation maximum that influences northern hemispheric temperature (and thus, due to land area, glaciation and global air temperatures) was thousands of years ago. Understanding this history of climate, the earth should soon be entering a cooling period, of which the "little ice age" of the middle part of the previous millennium may have been a precursor. So the recent warming stands in stark contrast with the expected response to decreased insolation in the northern hemisphere. What else might be driving a warmer climate? One answer is the increase in greenhouse gasses for which there is no recent proxy to understand its impact. Certainly over the last 200,000 years and likely over the last few million years natural CO2 concentrations have ranged between 200 ppm and 290 ppm. Natural CH4 concentrations were between 400 and 700 ppb. Present levels of CO2 are about 366 ppm and for methane about 1750 ppb.
We know that greenhouse gasses trap outgoing longwave radiation.(1) We know that increased levels of greenhouse gasses (CO2, CH4, N2O, and all CFCs) are due to human influence. We know the insolation in the northern hemisphere has decreased over the last 1000 years, yet, the earth is warming.(2, 3) Does this mean that without a doubt the earth's climate will warm over then next X years? Who knows? The earth is filled with positive and negative feedbacks and thus its complex nature. We do know that the earth has been MUCH warmer in its past so it can overcome the negative feedbacks.
Let us also not forget that global warming (a misnomer perhaps) will not necessarily be purely a phenomena of temperature but will also influence other aspects of the climate system such as storm strength, the hydrologic cycle, and the like.
I am not claiming that global warming is a clear and dry matter. None-the-less, just as climate scientists need to gather more evidence to show the effect that increased levels of GHGs are likely having on the climate (and ecological) system, so do the critics need to explain 1) how the climate system could go unperturbed by large increases in GHGs and 2) What alternate explanation is there for recent temperature increases?
Kenneth Mack
(1) Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 JE Harries, Brindley HE, Sagoo PJ, Bantges RJ Nature Volume 410 Number 6826 Page 355 - 357 (2001)
(2) http://www.ngdc.noaa.gov/paleo/ei/ei_image/nhem1400.gif
(3) http://www.ngdc.noaa.gov/paleo/ei/ei_millenm.html
2 & 3 from http://www.ngdc.noaa.gov/paleo/ei/ei_cover.html
>
> --
> James Heartfield
>
