2010-10-19 02:17:53How urgent is urgent?


When a scientists or activist says, "we need to do something about global warming", many of my skeptic friends say "it's not an urgent issue"...  we can take care of it later... 

Good point.  How urgent is this issue?

The latest email I have received is this one:


Among lots of inaccuracies in the article it raising questions such as, "how catastrophic" is Global Warming?  Maybe that hurricane or increased flooding in that area is related to GW but how do we know?  How urgent is the problem?  How long can we wait?  We have to find jobs and get this economy going before we can do anything about Global Warming (in the USA)...  etc...etc.... 

 I don't know how to answer this issue.  Sure, it's better to be safe now rather than wait.  It will cost us more money if we wait etc...

 But it does raise the issue in my mind about how urgent do credible scientists think the issue really is?



2010-10-19 04:55:10



The degree of urgency depends on which aspect you focus on:

- Coral reefs: One estimate I've read is that we could have a major wipe-out of coral reefs by 2050, due to temperature increase + de-alkalization

-  Sea-level rise: Time frame depends on what water level you want to worry about. Probably safe to say something like 7 meters in 200 years.

- My "favorite" threat is ongoing: Species loss by climate change. The number that comes to mind: about 20% in 150 years. But that's just an extrapolation: Once you start talking about that sort of number, the ecosystems can change in ways that are really not predictable. 

However, for a quantitative estimate: If we project a continued warming of 0.1-C/decade, that corresponds to a poleward climate shift of about 6 kilometers/decade, or to an altitude climb of about 16 meters/decade. How much of that can the ecosystems take?


And this is just when the consequences show up. But there can be a long delay as well. If we were to stop adding CO2 today, the Earth would continue to heat for quite awhile, because the oceans would not be in the right steady-state condition to have a stable temperature. Off hand, I don't remember whether the time frame to take care of the ocean delay is closer to 10 or to 50 years. In either case, the point is that we won't experience the full result of our emissions for some time after we've stopped emitting.

2010-10-19 09:16:00

Urgent in this case is commutative and conservative. Lots of little urgencies add up to a large urgency, a snowball of catastrophe. So the question is not really "how catastrophic is global warming" or "how long can we wait" but rather "how large will we allow the catastrophe to become?" 
2010-10-20 02:34:03Forbes article
Dana Nuccitelli

Interesting you mention the Forbes article - I read it a couple days ago and then got into an argument with a bunch of 'skeptics' in the comments :-)

My answer to the urgency question is that 2°C warming from pre-industrial levels is defined as the 'danger limit', and we're already committed to 1.4°C.  We need to cut global GHG emissions by about 50% by 2050 to have a good chance of avoiding that level of warming.  A 50% cut over the next 40 years is going to be extremely difficult, and the longer we wait, the harder it will be.  Thus there is serious urgency.

2010-10-20 03:14:25Comment
Robert Way

I'm wondering how we are committed to 1.4 degrees . I know from a mathematical sense that is the amount but isn't half of the current warming natural at this point?
2010-10-20 06:35:04Committed to 1.4 degrees
John Cook

The planet is currently suffering an energy imbalance of around 0.85 W/m2. Regardless of what has caused it, the planet will continue to heat 0.6 degrees until it reaches equilibrium and the imbalance is removed. As is my understanding.
2010-10-20 08:43:46


Robert Way:

"...isn't half of the current warming natural at this point?"

What do you mean by "natural"?

2010-10-20 10:38:06Comment
Robert Way

I mean we have attributed the early to mid 1900s warming to natural causes, solar irradience, AMO, low volcanic activity. Part of the component of the current warming has been attributed to multidecadal climate variability associated with the AMO (paper posted by john a while back) and then when we consider that every roughly every 1000 years we get a spike in temperatures (similar to the MWP and RWP ) I find it hard to buy that was can consider the 0.8 we have already received as being due to CO2. Half of it maybe but the full 0.8 is a little far in my view. So then do we really have 1 degree left of already committed warming in that case or is there more to this story.  I think what i've been told is that as much as 0.2 of the warming could be due to millennial scale solar variability.
2010-10-20 10:48:12Comment
Robert Way

This does not at all change my views on climate change going forward, I believe that we will see a large temperature increase with the increased usage of CO2 but it does make me question attribution of all the warming to CO2...
2010-10-20 10:50:05

I've also heard of a large attribution of warming due to deforestation and other land-use changes.
2010-10-20 11:13:24
Robert Way

Lets consider this is north american temperatures recorded by 700 pollen sites


The present is about 1955 I guess, but the problem is its pollen data so you just can't latch on the instrumental record onto it. But you see my point, can we really say that current warming is fully CO2 attributable? We are probably close to the maximum "hypsothermal" now but who knows really, pollen data is too low resolution (100 years).

2010-10-20 12:14:54
Rob Painting
Rob, and pollen data for the Southern Hemisphere over the same period?.
2010-10-20 12:41:37Comment
Robert Way

This isn't about the hemispheric extent of the MWP. This is only north america so of course it will be noisier than the hemispheric averages. But there is evidence (see moburg et al. 2005, lunqvist 2010) that natural oscillations are contributing to the current warming. The claim that the MWP was not global is something that I find a bit difficult to believe, but to suggest that it is as warm as it is today is obviously incorrect. All i'm trying to put forward is that there's not a neat and tidy 0.8 CO2 rise in the current warming and even a paper john showed before seems to argue that there is multidecadal variability contributing to the current warming.
2010-10-20 13:19:21
Rob Painting

This isn't about the hemispheric extent of the MWP.

I didn't mention the MWP, until now. I was merely interested in the global pollen data over that period. Showing just the North American pollen data gives no idea of the global extent. 

But there is evidence (see moburg et al. 2005, lunqvist 2010) that natural oscillations are contributing to the current warming.

I'm not arguing that natural variability would be somehow magically put on hold. Teasing out the anthropogenic portion is indeed difficult, because anthropogenic contributions, such as sulfur dioxide emissions, work in the other direction. I agree with you, it's not a "neat & tidy" number.

The claim that the MWP was not global is something that I find a bit difficult to believe

Perhaps, I'm not well read enough on that topic to offer any informed comment. All I know is the meta data analysis carried out by Mann & co. seems to suggest that it wasn't global. And I'm aware of a few papers that show warming in various regions, however they occur centuries apart.

seems to argue that there is multidecadal variability contributing to the current warming.

So we're probably talking about the ocean response in many instances?. 




2010-10-21 03:25:30Comment
Robert Way

We're talking about oceans causing some of the warming.

Also my suggestion is to not trust Mann et al's global reconstruction as being definitive. But if you have seen it, there is a clearly prominent MWP spike. The understanding amongst the paleo community that I have heard of is that only after 1980 do we surpass MWP type temperatures globally.

Personally, I'm not a big proponent of aerosol theories but that's up for debate undoubtedly.
2010-10-21 09:08:13
Rob Painting

Don't worry Rob, I don't trust any of it (paleo research) to be definitive, just a reflection of our current understanding, which of course can change as further information comes to light. 

Why exactly are you so down on aerosols?. In regard to sulfur dioxide, the effects on the climate seem pretty clear, as witnessed by global cooling induced by the Mt Pinatubo eruption. And natural aerosols - they play a major role in the climate, for example the organic aerosols emitted by vegetation in the Amazon have an impact on precipitation in the region, and also affect the seasonal distribution of rainfall. Then there's the aerosols emitted by phytoplankton to the atmosphere. My own supposition is that we'll find aerosols have much more of an impact on the climate than anticipated.