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It's not an estimate. It's an absolute measurement of the CO2 content of atmospheric gas trapped in bubbles within layers of ice.

Your comment about being impossible to be 100% certain is a red herring. We could say the same about the sun rising tomorrow. Nothing has a 100% certainty guaranteed.


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Well we can say that with reasonable good accuracy - using proxies, and I've never come across anyone as yet who has disputed the proxies (Deuterium proxies in the case of temperature).  Even climate denialists love to quote ice core data.

As far as the future is concerned, it will depend on the Greenhouse gas levels in the atmosphere, the solar irradiance and other factors such as whether we get a super volcano.

Of course there is a chance that we'll get a super volcano, but I wouldn't bet on it.  THe last one was about 74,000 years ago.

The solar irradiance is pretty predictable. If anything, it has been dropping off slightly in the last 30 years.

But the point is that the crux of the argument I've been making has nothing to do with past CO2 levels and paleotemperatures. They serve as confirmation, nothing more.

I've been talking about the fundamental physical properties of greenhouse gases.  

OK,

In that case you've already said that the temperature increase has been about right for a doubling of CO2, and (as I understand it) you accept that we haven't had a doubling of CO2 since 1850.

The difference is due to feedbacks.  There are many ways we can confirm the approximate magnitude of the feedbacks. Mount Pinatubo also helped us to understand that.

OK -  For a business as usual scenario, we'll end up doubling the CO2 from preindustrial levels by about 2050 - or 2070 for the very best scenarios (where we've managed to transition to renewable energy sources).

Let's get one thing straight (you might know it already) - I'm not a commie. I don't want to redistribute wealth. I don't want to donate huge sums of money to inept governments. I'd rather keep what money I make (thank you very much) - and  I've never taken a government handout at any stage of my life.

I am in a position where I understand the science, and I would prefer to avert the kind of severe problems that we'll be facing.

The solution to this problem is to build renewable energy infrastructure and to maintain an active economy so that we can have the resources to tackle this problem. Some of the solutions to this issue will be high cost.

Technology has changed in the past and it will change in the future.  Our civilisation has landed man on the moon and delivered an information superhighway.

I'm not about to see all this go to waste. I want to see space exploration in future. I want humanity to start colonising space and expanding throughout the galaxy. That's my dream, and the main reason I'd sooner see humanity survive.   

Now in some respects, it's immaterial what you actually believe. As long as you want to see less reliance on fossil fuels, that's good enough for me.

I'm just trying to explain teh scientific basis, because there are people out there who have taken what is a relatively straightforward issue and confused people big-time.

Not quite.

The CO2 level has increased from 280ppm to say 387ppm between 1850 and the present. That's only 37%, or roughly 1/3 of the way towards a doubling.

The warming due to CO2 for that increase should be approximately 0.3 degrees C.  (It's not exactly linear by the way.) That's based on 1750 rather than 1850, but the difference is small.

Observed warming was around 0.8 degrees since the start of industrialisation (1750 is most often quoted).  Do you want me to show the calculation?

Now that method results in a climate sensitivity of 2.1, but it's not quite that easy though, because there are all kinds of other effects including aerosols and variations in solar irradiance.

You can also use Ice Age data to come up with a similar value for Climate sensitivity.  Some papers show large variations. For example, Ganopolski and Schneider von Deimling (2008) show a range of 1.3 to 6.8 °C for climate sensitivity determined by this approach.

A question for you - Which greenhouse gas is most responsible for the warming of the Earth? Can you put a figure on it?

gizmo_2655 wrote on Sep 6^th, 2010 at 3:47pm:


Once again, it's not primary evidence. The primary evidence is the physical property of the CO2 molecule and the water molecule to absorb Long Wave Infrared radiation and re-emit it at all angles. Now that can be measured.

The past temperatures are........ well over and done with.  The paleo data just serves as additional confirmation of climate sensitivity. The actual climate sensitivity is the most difficult thing to measure accurately.

If you want a better confirmation, you just need to actually measure the outgoing Longwave Infrared that's escaping into space. You can plot that against wavelength, and there you can see exactly what's happening over time. We can do that of course, using satellite data.

2. OK - Explain what you mean.

3. Answer my question.

gizmo_2655 wrote on Sep 6^th, 2010 at 5:17pm:


I don't know about your time frame, but I can guarantee that when this cycle of Global warming is finished, the Climate WILL REVERSE & GO INTO THE NEXT ICE AGE.

The questions are we slowing or speeding that event from becoming reality and which option is worse Warming or Cooling?

perceptions_now wrote on Sep 6^th, 2010 at 8:06pm:



Cooling is very much worse than warming...

And the time line was conjectural....pick any date you like...

I used 2015 simply to make the point that we cannot tell what will happen in the future.....

muso wrote on Sep 7^th, 2010 at 8:35am:


"based on current information"...yes and that's exactly my point...

And if the current information is incomplete or the factors change??
Remember, chaos theory and the 'butterfly effect'...

gizmo_2655 wrote on Sep 7^th, 2010 at 8:46am:



Good point, a moth just broke wind in Siberia, and the resultant gale has blown your objections away.

Perhaps the denialists are just following Christ's last instruction, shouted down to them as he floated bodily into space,
"Don't do anything , 'til I get back."