[richy (OP)]

Hi first post, regular listener to the podcast.

This has always bugged me, in the past there were no ice caps, the average temperature of the Earth was 22°C whereas now its 12-13°C. So what's the problem? The Earth has been hot in the past why are scientists so worried? We'll be alright won't we?  []

[LeeE]

There wasn't a problem for us then because we weren't around then.  We probably won't be alright because our food chain is not only highly dependent upon the climate but has also been customised to be more efficient in the current climate and will probably be much less efficient if our climate changes.

[blakestyger]

We'll be alright won't we?  []

No, we not going to be alright.

You've seen the way certain nations have made a grab at the energy resources by going to war over them. Well that'll seem like chickenfeed when the sea really starts to rise and the landgrab starts. And that's just the start - there will be conflict over water and food as well as raw materials.
Humans were successful in the past because they thought short-term (fix it now, go to the next thing) but this will eventually be our collective undoing.

[Evie]

I have often debated the exact ramifications of global warming with myself (consequently, I never seem to lose the argument  []), and my conclusion is that it probably would not lead to the extinction of human beings, but that there would be a lot of conflict while things were drastically changing. Don't forget, most major cities are built near oceans and rivers, so many of them will have to abandoned eventually. Agricultural areas will shift and some smaller countries may cease to exist entirely.

[richy (OP)]

Thanks very much,

I agree it will be a very unpleasant place to live if the sea levels rise especially from the inevitable wars over land grabbing, but I also agree Humans as a race won't become extinct, we are just too adaptable.

I am also interested in the idea of thermal runaway, like what has happened to Venus, could this happen to us? Was the Cretaceous period hot because of excess CO₂ or another reason?

[Evie]

The only other consideration that could make things much more difficult is a variation on the "snowball earth" theory. Some scientists think that warming of the oceans could cause the thermohaline circulation to shut down (causing ocean currents to stop), making northern latitudes that rely on warm-water currents colder (like the UK!). As more ice built up in the extreme north and south, more sunlight would be reflected from the earth, making it colder, causeing the ice sheets to progress, etc., etc., etc. Eventually, it would result in a completely ice covered planet. Life would suck then!

http://www.cgd.ucar.edu/cas/adai/papers/Dai_etal_THC_JCL05.pdf

[frethack]

No, we not going to be alright.

You never know...the sun could decide to take another vacation (a la Maunder/Dalton/Sporer/Wolf/Oort minimum) and we could be plunged into another Little Ice Age, sparking a HUGE land grab as the northern latitudes become uninhabitable throughout most of the year.  Or, if we continue to warm well past our current temperatures we might even reach the climatic conditions of the Holocene Optimum (also, conveniently coincided by a huge increase in the 22 year solar cycle), when the Sahara supported widespread vegetation, rivers, lakes, and animals.  If we dont quite reach HO levels, we could see temps comparable to the Medieval or Roman Climate Optimums (again, large solar maximums...is there a pattern here?) when grapes grew in England and Nova Scotia (Roman and Medieval), North Africa supplied much of the Roman Empires grains , there was enough food to feed armies of workers who built the temples, cathedrals, and canals, and the Norse thrived on the beautiful, lush pastures of Greenland (Medieval).

...or the Atlantic meridional overturning circulation could slow down enough to plunge us into an ice age.

The climatologists that Ive had opportunity to speak with have all said the same thing:  We dont know

Was the Cretaceous period hot because of excess CO2 or another reason?

Here are estimated CO2 levels throughout the past 600 million years:



Keep in mind that there were Ice Ages at about 680 ma (Second Snowball Earth episode), 450 ma (Ordovician/Silurian ice age), 280 ma (Carboniferous/Permian ice age), 150 ma (Jurassic/Cretaceous cooling), and the ice age in which we currently find ourselves. All of these have CO2 estimates anywhere from an excess of 5000ppm all the way to 185ppm.