Climate change: what would make me change my mind?

February 23, 2007 at 10:05 pm | In Answer, Climate challenge, Climate change, Global warming, IPCC | 7 Comments

Similarly, for those who do accept the scientific consensus, what evidence would make you an agnostic?

As a member of the public who accepts the scientific consensus, because:

I have respect for the majority of the world’s scientists,
I accept the peer-review process as the most thorough, practical way to make an informed assessment of the scientific literature,
and I trust that the objectives of the IPCC are not being undermined by a conspiracy,

my mind could still be changed. Here’s how.

I would change my mind to think global warming were a topic best left to the realms of scientific research—not yet proven, not newsworthy, and certainly not worth worrying about—if the IPCC made a statement and supported it with indisputable, independently verifiable evidence, along these lines:

Variations in the climate system continue to be observed. To date, the physical science underlying the processes responsible for this is not understood. No scientific model has yet been developed to reproduce and thus explain such observed variations to any level of accuracy over any timescale of interest. Warming and cooling of the climate system continue to be observed, as is now evident from observations of increases and decreases in global average air and ocean temperatures, widespread melting of snow and ice in some regions concurrent with widespread accumulation of snow and ice in other regions, and rising and falling global mean sea level.

The IPCC would have to state that such a statement superseded their actual statement on February 2, 2007:

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.

I would also change my mind to think global warming due to human activity were a topic best left to the realms of scientific research—not yet proven, not newsworthy, and certainly not worth worrying about—if the IPCC made a statement and supported it with indisputable, independently verifiable evidence, along these lines:

A proportion of the observed increases and decreases in globally averaged temperatures since the mid-20th century could possibly be due to the observed increases and decreases in anthropogenic greenhouse gas concentrations. However, there are no clear trends and no clear connections between observations and potential causes, as scientific models are unable to replicate and explain these conditions. Therefore, assessments cannot be made with any accuracy as to the proportions, effects and possible impacts related to anthropogenic greenhouse gas concentrations compared with other environmental events, drivers and conditions.

The IPCC would have to state that such a statement superseded their actual statement on February 2, 2007:

Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

There are 2500+ scientific expert reviewers, 800+ contributing authors, 450+ lead authors from 130+ countries, who have worked for 6 years to produce 4 volumes (of which the recent report released in Paris is the first) which will be combined into a single IPCC report “Climate Change 2007″ later this year. This larger assessment report is the fourth to be produced by the IPCC and is referred to as AR4.

In order to change my own mind, I would have to be convinced that a majority of these people—scientific expert reviewers, contributing authors, lead authors and their 130 governments—have changed their minds too.

P.S. When I see at least half of the dots on graphs from NOAA, NCDC, and other scientific researchers coloured grey (or even colored gray ), or at least some balance between blue and red dots, on maps such as these:

I would consider anomalies in the global average air and ocean surface temperatures to be just one component of the natural variability of our climate system, so no worries

7 Comments »

RSS feed for comments on this post. TrackBack URI

Very nice post, inel. I’m impressed.

Comment by reasic — February 24, 2007 #
Hi inel,

‘The Coffee House’ has been on the Anti-trident march today in London. Thought you & your fellow bloggers might like to see some pictures from the frontline;

http://environmentdebate.wordpress.com/2007/02/24/the-coffee-house-woz-there/

Comment by matt — February 25, 2007 #
Hi matt,

Thanks for this update! I particularly like the picture of the dear old GOAT (only in Britain … )

Can I use that shot to link to you, please?

Comment by inel — February 25, 2007 #
Yes, that’s fine.

Comment by matt — February 26, 2007 #
Since 98 % of greenhouse gases (those capable of absorbing infrared) are water vapour, with less than 2 % CO2, I’d say it defies common sense to say that CO2 can have any effect on global warming. Whats more water vapour is certainly not anthropogenic !

Comment by RICHARD SHEPHERD — April 3, 2007 #
Hello Richard,

Thanks for your comment. You are right that water vapour makes up a far larger percentage of the greenhouse gases (GHG) than any other gas alone.

Please tell me which climate scientists provide you with the 98% figure for the water vapour as a percentage of total GHG. I have not seen that specific number quoted in the scientific literature.

Here are a few more points to take into account:

* A GHG may occur naturally, and/or may be anthropogenic.
o You are right that water vapour is not anthropogenic: if we humans add water vapour to the air, the water cycle brings it back down to us in the form of rain, sleet or snow. It reaches its own equilibrium.
o Water vapour occurs naturally and provides a large proportion of the natural greenhouse effect. As such, water vapour plays a large natural role in increasing global surface temperatures by about 33 degrees Celsius, so the Earth can sustain life as we know it.

* A GHG may be a radiative forcing (negative or positive) or may be a feedback.
o A positive forcing warms, and a negative forcing cools, the atmosphere.
o Unfortunately, with the climate situation as it is now, a positive forcing is a negative (i.e. non-beneficial) warming effect.
o A radiative forcing changes the radiation balance of the atmosphere: this happens naturally all the time.
o The term radiative forcing is also defined very precisely by the IPCC. In simple terms it means an externally imposed change in the radiative balance, such as occurs with anthropogenic GHG causing AGW.
o A feedback is a secondary effect, while a forcing is the dominant operator (of which there are several, but CO2 is one of the main GHGs for which we need to reduce emissions, and the IPCC now refers to such anthropogenic sources as drivers for climate change).
o Water vapour is an important GHG, and is the main absorber of radiation, but it is a feedback, not a forcing, and certainly not a driver.

* Water vapour makes up about 80% of the GHG total by mass and about 90% by volume.
o Since percentage by mass and percentage by volume are not the same as radiative forcing, there are calculations that have been done by climate scientists to figure out radiative forcings and from those figures come estimates of the percentage of the greenhouse effect that is contributed by each GHG.
o The combinations of gases in differing proportions give a range of results, but climate scientists calculate water vapour provides between 36—66% of the greenhouse effect, and together with clouds those numbers reach 66—85% of the greenhouse effect.
o The scientific literature reports CO2 providing 9—30% of the total greenhouse effect.

The point you are missing, or misleading people by ignoring, is that of climate sensitivity to “slight” changes in temperature. That is crucial in terms understanding anthropogenic global warming (AGW).

Nobody is disputing that the natural greenhouse gases have done a nice job of keeping much of the world pleasantly warm with fairly consistent growing seasons

What is at issue is the way in which human activities have added GHG to the naturally occurring mix and we have upset the balance by raising temperatures by tiny—but extremely significant—amounts over decades and are now seeing the effects.

Worse still, there is a delay in the climate system that means we know that some GHGs we have added to the atmosphere have yet to take effect. Here’s another difference between water vapour, carbon dioxide and methane: changes in H2O concentrations in the atmosphere are only effective over days, whereas the negative warming effects of CO2 persist for a century or more and the negative warming effects of CH4 persist for decades. Therein lies our time-lapse problem. We can see that we have already added too much GHG responsible for positive radiative forcings to the atmosphere to expect concentrations and hence temperatures to “return to normal” any time soon. We have to mitigate our carbon emissions and adapt to climate change now.

Further information is available at RealClimate here.

Comment by inel — April 3, 2007 #
Good response, inel. I would only add that the 98% number, from what I can tell, originated from Dr. Lindzen, and without any evidence or verification for such a figure. Richard, if you have any such supporting information, it would be helpful to supply that. As inel pointed out, water vapor, even when combined with clouds, have a maximum effect of about 85%. I’ve also posted on a similar question here.

Comment by reasic — April 3, 2007 #