There is a complete lack of understanding about how the Earth's climate has changed. At the end of the Cretaceous period the mean global temperature was about 8 deg. C hotter than today. Since then the climate has cooled and due to this cooling the polar ice caps formed, expanded and retreated at least four times. The last retreat started 12,000 years ago and continues today. We are now in an Inter-glacial warm period. None of these climatic variations have been attributed to atmospheric carbon dioxide. For the last 8,000 years the mean global temperature has been relatively stable around 15 deg. C with minor fluctuations giving rise to the 14th to 19th century mini-ice age, and a drop in mean temperature of about 0.5 deg C compared to 8,000 years ago. Throughout this same period to 1850 the atmospheric CO2 rose by nearly 12% from 255ppm to 285ppm.

So why all the hysteria? CO2 is not the culprit.

For the complete history of global warming, see this:

http://www.aip.org/history/climate/index.html

I think it's a little more complicated than you are making out.

Lucibee, I am trying to keep the argument on this CO2 global warming hysteria, a topic that from my own knowledge has lead me to believe is seriously flawed.
Yes it is more complicated, especially if you start to incorporate Milankovitch cycles along with the 100,000 year oscillation.
Do you believe that global warming is due to human activity? If so why?

Geoman,

Can you explain to me what effect the change in the distribution of landmasses may have had on our planet's climate patterns?

Cobblyworlds,
No, can you tell me. It must be complicated when you consider how the continents have broken up, drifted and grown from the Early Cretaceous to the present.
Do you believe that human activity is causing climate change? And Why?

You spotted my trap then. Well done.

(I was alluding to the hemispheric disparity of land/ocean cover and it relationship to Milankovitch forcing and ice-albedo feedback in initiating ice ages.)


1) Solar activity changes match fairly well to past changes in global average temperature (GAT). Various studies.

BUT

2) Since 1950 Cosmic Ray Flux - no trend (Climax). Since 1976 no change in Total solar Insolation (TSI) (Frohlich 2006).
yet

3) Since 1975 3 decades of continual GAT increase, total ~0.6degC, ~0.2degC/decade. (NASA GISS)

4) Stratospheric cooling, indicative of enhanced greenhouse effect (Strato warming would be implied by TSI increases).

5) Studies of increase of CO2, e.g. Seuss effect - show increase is anthropogenic in origin. Acidification of oceans - thus not outgassing from oceans.

6) The increase in ocean heat content implies a radiative imbalance of ~1W/m^2(watt per metre squared), which is too big to be down to internal climate processes.

7) Proven ability of the models to project into the future (Hansen et al 1988) and ability to hindcast proven. Studies like Meehl et al (Additivity attribution) show that the warming post 1970 is due to enhanced greenhouse effect.


So we have a period since the 70s in which the Sun has been ruled out as a warming factor. During which a ramp-like increase of temperature has occurred. And models attribute this to increasing CO2, which we know is due to humans.

The warming of 0.6degC since the 1970s is the start of the anthropocene, and that warming is due to human activity, mainly CO2 emissions.

As a scientific statement that would include some probabilistic qualification - each "is" would be "is very probably". But I'm an ex-sceptic who's learnt the science and really think that qualification is superfluous in every-day terms.

We are warming the planet. climate response likely to be about 3degC to twice pre-industrial CO2. In the future it'll get warmer, but as to specific impacts - we'll find out won't we?

Cobblyworlds,

Many thanks for your recent posting. Much appreciated. I will mull over what you have sent.
This is my first time on a community channel, quite enjoying it. It takes me back to my old university days.
On word of warning from my own experience in the geophysical field. Models do not give complete and unique answers and are still open to interpretation. They depend completely on the data input. If the model is non-linear, as I suspect the climate one to be, small errors can become greatly magnified.
One question, do you know if the climate model you mention has been used to inverse model the climate to see if it "predicts" the past as a check on its validity? You can not check the results of forward models, but there is much historical data that can be used. Is this what you call "hindcast"?
Got to close now, be back tomorrow.

I'm known, hated by some, for my long posts.

But here goes again.


Hansen 1988, see a very basic run through here.

As you can see it was hindcast, and yes a hindcast is a backwards run to check validity against known data.


I know models are to be treated with great caution, but that has to be qualified.

I would not trust the models to project detailed regional impacts well into this century. There is plenty of information about problems with small scale agreement. However there is reason to accept that models are of value on large scale measures like global average temperature and total column water vapour.

So for gross attribution studies I'd take the results seriously. e.g. http://www.globalwarmingart.com/wiki/Image:Climate_Change_Attribution_png