Climate change question - how much has the climate actually changed?

http://www.ipcc.ch/ would probably be a good place to start.

One of the reasons that people call it “climate change” and not “global warming” is because there is more going on than just warming. In some places, the environment may get cooler. Weather patterns are also changing, and some places are getting drier, while others are getting wetter. Lots of stuff is changing.

What worries scientists isn’t necessarily the amount it has currently changed, but rather the rate at which it’s changing. Earth’s climate has changed dramatically in the past many, many times. But such changes tend to be slow, so life has time to adapt. What’s going on now is looking more and more like a sudden, mass-extinction event.

i think the most urgent issue facing us is climate change, global warming, whatever you want to call it. the lives and well being of our children are seriously at stake and we all need to do something for the future well being. climate change like evolution is not a theory…it is a fact and we must do something about it.

The worst-case scenario of a drastically changing climate would be mass-extinction. When climate, and as a result ecosystems, begins to change faster than animals and plants can adapt they start to disappear. On a global scale this can cascade into a level of extinction that grows exponentially.

It’s happened before too. At least 5 mass extinction events have occurred in Earth’s past – the worst of the 5 was around 250 million years ago when roughly 95% of all species went extinct. Would humans survive such an event? Probably not.

More evidence suggest that the extinction of the dinosaurs was also partly caused by a rapidly changing climate.

As indicated first we either have to talk in global averages, or specify a region. Then we have to narrow the discussion to which aspect of the climate we are talking about. For instance, growing season length, mean winter temperature, mean summer precipitation etc..

But quickly, over the last century global temperatures have increase on average around 0.76 degrees celcius. Sea level rise slightly less than 2mm per year. Remember that these averages can hide significant shifts in a given region.

For the future, the strength of high wind events in some regions is increasing but there is still some question as to whether the frequency of events is changing. Overall rainfall is increasing globally but unfortunately this seems to be occurring as higher intensity rainfall in wetter areas, with increasing drying in those areas that are dry. So the Mediterranean, the Sahel, and Southern Australia gets drier (they need the rain), whereas Sweden and Northern Australia for instance may have more intensive flooding.

At the recent climate conference in Copenhagen last month it was emphasized that although our capacity to predict temperature changes for a given greenhouse gas emission was relatively accurate, our previous attempts at predicting sea level changes has been limited. With better measures and understanding of ice sheets and glacier loss, we now know things are occurring far more rapidly than had been predicted. The estimates I saw were for rises of approximately 1 metres this century even for low emissions scenarios.

There is serious concern regarding water availability in catchments extending from the Himalayas. Concern regarding salt water inundation of low lying areas.

Current projections suggest that at 450ppm atmospheric co2 concentrations (we are likely to hit this as this roughly equates with the European Unions target of 2 degrees global warming and no more) many reef building organisms may no longer be capable of balancing accretion rates against erosions rates, as the associated increase in ocean acidity reduces calcium carbonate creation. Thus potential loss in the current structure of many reefs around the world.

In simple terms, humanity relies on the services ecosystems provide and ultimately ecosystems are structured by climate, as are global sea levels, ocean acidity, and storm patterns. We are changing the climate to an extent that may induce feedbacks (release methane stores from peat, release vast amounts of carbon locked in degrading forests, reduce ocean absorption of carbon). There are unknowns but all the peer-reviewed published evidence suggests that the further we travel along this path, the more extreme the changes will be and the costlier the solutions will need to be. Work by Stern and others indicates (even with recent revisions) that the costs associated with mitigation are far less than the costs associated with adaptation. In other words, it is cheaper to stop the emissions than to try to live with their consequences…but the more we emit the higher the costs and the less nature does for us (natural sinks appear to be declining in their efficiency…currently they absorb about half of our emissions).

I also recommend that you download the summary for policy makers AR4 report if you want a good overview (Quingu has the link above to the IPCC, summary report down the page as a PDF). But remember that the data that was used for this 2007 report is really the best of knowledge from 2005, so it is dated. It should be seen as a conservative estimate, as the knowledge gained in the last four years only emphasizes the seriousness of the situation.

@btko, I actually think if anybody is capable of surviving a Permian-style extinction, it would be us humans. I think that may be raising the alarm a little higher than warranted.

However, while we will almost certainly survive a worst-case scenario of global warming, little of our current lifestyle or civilization would remain intact. It would probably usher a new “dark ages,” at least. We’ve seen that happen numerous times in human history to various civilizations who abused their environments (the Maya are the most famous).