Posting in Environment
Climatologist Kim Cobb is working to build better climate forecasts.
When Georgia Tech climatologist Kim Cobb isn't busy raising her four young children, she spends her days scuba diving for tropical coral samples and developing models of El Niño events. That's because our current climate change models aren't good enough -- and Cobb is working to build better climate forecasts. On her mission to understand climate change, Cobb has been lauded for her work by the National Science Foundation, PopTech and other groups.
In a recent interview, Cobb explained what the recent past tells us about climate change, why precipitation matters and what it means to be "20 percent Indiana Jones." Below are excerpts from our talk.
Your goal in a nutshell is to better predict the progress of climate change. How do we do that currently and why isn't it good enough?
It's probably never going to be good enough. We'd like to always know important things better, so I'd couch what I'm going to say with that caveat.
We'd like to know about expected changes in precipitation, for example. We use large computer simulations of the climate system, including the ocean, the atmosphere, land and ice. We have some fundamental equations that drive the exchanges between these components of the climate model, such as how water moves from the ocean to the atmosphere. Simulating precipitation is very difficult. We rely on some parameters and shortcuts of physics in coding precipitation into models. It's something we need very high resolution models to do. We have a fundamentally incomplete picture of the physics that drives clouds and precipitation.
This ends up being a large uncertainty in the kinds of global climate models that we run in these 100-year projections. You can see this when you look at projections from a multi-model perspective. The suite of models don't necessarily agree in the sign of precipitation change for any given location on the planet. If you want to get down to a region, like the western U.S., you would be even worse off in looking at expected changes. This remains a strong limitation of our current suite of what we call models that are run in the 100-year simulation modes for future climate change. There are a couple dozen of these sophisticated climate models we use for projections. Our general assumption is that when they tell us something collectively, we believe that. Unfortunately, this is not one of the things they do very well.
What are you doing to improve climate model forecasts?
I'm looking to challenge the models to simulate climate changes that occurred in the distant past. Some of these are very large climate changes. But more often my work focuses on climate changes in the very recent past -- the past several thousand years. We resolve climate signals we believe may relate to a forced signal in the climate system caused by, for example, volcanoes. We look for a response to these changes. If we see it, that's an important answer. If we don't, that's another important answer. For the first time in history, the models have been run in paleo-simulation mode. That's a huge step forward for the climate community. Our best models are being explicitly tested with forcings from the more distant past. We have simulations from 6,000 years ago, from 1,000 years ago. They include solar volcanic variability, changes in carbon dioxide. They include this suite of forcings and we can look at the responses and compare them to actual data.
I generate the data that can be compared to these paleo-simulations. Increasingly, I'm becoming involved in doing those comparisons myself. I can compare apples to apples. It's exciting.
You'd think temperature is the most important piece of the climate change puzzle, but you argue that rainfall is critically important. What does it tell us that temperature doesn't? What does something like last summer's drought tell us?
Precipitation is a difficult beast in climate. It is highly variable. This is apparent to all of us. Ocean temperatures have a profound effect on precipitation distribution, statistically speaking. We can't see this on a climate change 100-year timeline, but we can certainly see this when we look at something as basic as hurricane generation. When do we have hurricanes? When the seasonal temperatures are the warmest they're going to get in the Caribbean. A good example comes from the El Niño phenomenon where warmer temperatures drive heavy precipitation along the eastern United States. That's a fairly subtle change in sea surface temperatures, yet it affects precipitation patterns around the globe in fairly predictable ways. This tells us that temperature is a primary control of precipitation patterns. Our challenge is to understand what drives the longer-term variability in precipitation.
Droughts are not unprecedented if you look at tree ring records as proxies for past precipitation. You can see these episodes of mega-droughts in these records. We can surmise that some of these may have been caused by changes in ocean temperatures. This [recent] mega-drought might have been caused by global warming, but all the ones in the past are presumably [related to] natural variability. It's something our planet does. It tells us that today's levels of drought are certainly not without precedent. Our job is to try to understand how these mega-droughts were caused. We don't have an answer for that right now, but it points to the importance of marrying our best paleo-climate data with our best models that can help us understand what causes drought in this region. That's a very promising avenue for improving projections of precipitation.
In the bio for your Twitter feed, @coralsncaves, you describe yourself as "20 percent Indiana Jones." What does your fieldwork entail?
I'm a field junkie. I have two primary sites in the Tropical Pacific with my coral work and in Borneo with my cave work. That puts me in a rare breed of scientist who is willing to fight through Third World bureaucracy and a lot of heat and rain and bugs to pursue climate records of unique value in reconstructing El Niño. These places have very large climate signals associated with El Niño events. I'm one of the only people knocking down these beautiful, difficult places in pursuit of these records. We've gotten quite a few interesting records out of these sites, which challenge dominant paradigms. You get to scuba dive and sweat and curse. You get the reward after three or five years of working on these records of producing something that is profoundly different.
You've said scientists haven't sold to the public the idea that CO2 is warming the planet. Why haven't they?
There are so many different explanations. From my own perspective, we have stressed impacts so much more than we have stressed the fundamental sets of observations that underpin that simple statement: carbon dioxide is warming the planet. We've relied on a communication that's built from impacts because we want to move people to act. The simple statement that the Earth is warming because of carbon dioxide doesn't seem necessarily like it's going to change hearts and minds. Where are the dollar signs? I actually think it might be enough to win hearts and minds. That's a pretty mind-boggling concept: that we're warming the entire planet. If people accept that as a scientific fact, that has immediate impacts that would be clear. For example, sea levels will rise. There's no physical way around that conclusion if you accept the premise that CO2 is warming the planet. We've sold short the average human's reaction to that piece of information.
As a climate scientist, I feel that if I can convince people through the bounty of evidence that CO2 is warming the planet, I stop. It's a huge victory for me. In order to move this debate forward, we're going to have to have a different set of toolkits and a diversity of voices. I try to get a very simple, one-dimensional, strong message across.
Photo: Kim Cobb / By Zafer Kizilkaya
Oct 21, 2012
"we have stressed impacts so much more than we have stressed the fundamental sets of observations that underpin that simple statement: carbon dioxide is warming the planet." "As a climate scientist, I feel that if I can convince people through the bounty of evidence that CO2 is warming the planet, I stop." It sounds like she feels there is not enough hard evidence right now. She wants to believe, but she has questions and is willing to do her own research to get them. An open minded scientists is a good thing.
This was a good interview with an active climatologist who is doing field work to get more observations of events and the effects. Part of the problem with communicating research information is that it is hard to present that information in a way that nonscientific folks can understand, especially when that information is counter to what they have learned.
i live in a small town in Alaska, and remember long-deceased elders making observations such as the height of the wild grass indicates how much snow will fall the coming winter. They also shared memories of weather events we might consider as 100-year, such as floods, but it was in their lifetime; our scientific research would do well to tap into such knowledge, or do we consider all stories baseless. . .
Why is that? How about the fact that they have discarded data that doesn't support their theories, manipluated other data, and scoff at and ridicule anyone who dares to ask questions? She is right about one thing; out climate models aren't good enough. The certified meteorologists in Austin all missed the forecast last week... by a mile. I have some simple questions for her. 1. At what point in earh's history was the global climate at it's optimum? Was iit during the last ice age? Was it during the 1930s during the U.S. Dust Bowl? What it last winter when eastern Europe had record cold? Was it the winter of 1941-42 when the USSR had their most severe winter? 2. Since the last ice age, hasn't the earth been getting warmer pretty much ever since?
[i]It sounds like she feels there is not enough hard evidence right now.[/i] Not enough hard evidence for what? That CO2 is causing warming? She is unequivocal about the fact that increased CO2 is causing warming.
In my reading this article, the author seems to be clear in her strong conclusion that humans are warming the planet. She thinks her job is to convince people that this is the case, and she is willing to stop at that because she can leave solutions to others. I agree with her thinking. We need to remove the question of whether humans are causing global warming from the political discourse. That humans are causing warming is a fact.. How to solve the problem is a very worthy subject for politics. Liberals may want more regulation or cap and trade. I could see that conservatives would want (1)more market oriented solutions (2)to depend more on voluntary efforts of individualsand (3) perhaps provide the revenue for income tax cuts with a carbon tax. All of these solutions help and they all can be debated. I would like it if she would actually respond to these posts.
[i]She is right about one thing; out climate models aren't good enough. The certified meteorologists in Austin all missed the forecast last week... by a mile.[/i] LOL, what does meteorologists missing a forecast have to do with climate models? The answer is not a thing. You open yourself up to ridicule when you say something like that because it demonstrates how little you know. 1. There is no optimum climate for the Earth but there may be for human civilization. Warming is already causing some disruption and it's only going to get worse until we get serious about it. 2. No, the Earth hit a temperature maximum during the Holocene Climate Optimum about 8,000 years ago. Since then there's been slight cooling trend, until the recent sharp rise. Natural causes of climate change are still trending for slight cooling. The stuff about discarded and manipulated data (to fix the science) is just urban legend material with little basis in reality.
I agree that scientists haven't sold the public, but I'm not surprised. Persuasion is not their field of expertise. Scientists typically talk with other scientists. But this issue is of such profound planetary importance that scientists are starting to worry about it and feel morally bound to try to communicate it. As for bb_apptix's points, there may have been some errors from time to time by some scientists, and there may have been occasional disparaging remarks aimed at deniers that were unwarranted. But there is no evidence of systematic effort by scientists to alter their results in any way other than to seek the truth. On the contrary there is a well documented systematic disinformation and confusion campaign going on by fossil fuel interests with millions to spend. The fact is that there is overwhelming consensus among the scientific community that humans are increasing co2 concentrations which are in turn warming the planet. The warming since the last ice age has been dramatically accelerated with the increased atmospheric co2. The optimal climate? I don't think we know. Clearly a little bit of warming can be dealt with and for some may be a good thing. We can say that the temperature has been in a pretty tight band for most of human history, and we are in danger of getting outside that band very soon. We came onto the scene and learned to live and prosper with a climate that was reasonable stable. We will soon be in uncharted terrritory. I might ask, why do you think we will like a much warmer climate? Shouldn't you stop your carbon pollution untill we can all agree we want the change that you are producing? Just because you want to go on polluting, are we required to just let you do it because you want to? Sounds a little like the second hand smoke discussion to me.
From what I have read, she seems to believe warming is happening now, but much of her research is focused on how warming happened naturally in the past and how does that compare to today. Most global warming scientists ignore some of the past because it often conflicts with their theories of the present. She seems to ask the tough questions. What caused the historic warming? Are there differences in how rapid or gradual the temperature change was during various historic temperature cycles? What natural events caused some historic cycles to be rapid and others to be slow? What really indicates mans actions as being the difference maker this time? She sounds like wants to put the science back in the discussion. She clearly recognizes there are legitimate questions that need to be answered. Surprisingly she directly names only the IPCC WG2 report on a short list of sloppy science from both extreams of the argument to be denounced. She calls for new standards for the collection of climate meta data. Obviously to address concerns over the integrity of the climate data kept at clearing houses like East Anglia. All I said was she seemed open minded and I appreciate it. And I still do. I look forward to seeing more of her work here. http://scienceblogs.com/usasciencefestival/2011/04/14/climate-change-reconstructing/ http://scienceline.org/2010/03/ancient-cave-formations-reveal-history-of-abrupt-climate-changes/ http://shadow.eas.gatech.edu/~kcobb/othertalks/PASI_cobb.ppt
The earth was at least as hot during the time of the dinosaurs over 65 million years ago as it is today. Much more recently, there's evidence arctic ice disappeared during the last interglacial period roughly 100,000 to 130,000 years ago (see http://www.tos.org/oceanography/archive/24-3_polyak.html ). Even closer to home, there's now tree-ring evidence that even during Roman times it was hotter than it is now due to orbital forcing (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1589.html ). Given that it was at least as hot in the past before humans released large amounts of carbon into the atmosphere as it is today, we can't rule out that whatever caused warming back then is also causing warming now. What the excellent interview reveals is a young science that is only just beginning to sort out all these questions. It's not ready to give us definitive answers to trillion dollar questions. People who say we should spend trillions on reducing our CO2 output (even though the recent shift to natural gas in the US has reduced our output to levels not seen since 1992) are making a big bet with someone else's money. We could even have a situation where most of the warming is not caused by CO2 but by natural processes we can't control. In this case rather than spending trillions on windmills and solar arrays, we would be far better off in spending the money to move people from the coastlines. Nothing in the interview indicates that climate science is at a stage where it can tell us what the real situation is -- not at these prices anyway. I would also point out to riverat1 that in relation to a discussion about climate models we had some weeks ago, this interview shows that scientists make a real effort to model the actual climate. Dr. Cobb spends a significant amount of her time trying to figure out how the actual climate works so it can be incorporated into climate models. Climate modeling is far from just running the models lots of times with random numbers that you claimed it was. We have to use a lot of approximations for relationships we just don't understand, but it's clear that scientists want to model the actual climate, not just throw dice.
What does the Earth being hot 65 million years ago have to do with the price of tea in China? The current ecosystem is not adapted for those temperatures and it would take 10's of thousands of years for it to become adapted. Also, there was no ice back then so sea level was around 200 feet higher than it is now. It's true that Arctic Sea Ice disappeared during the previous interglacial. Sea levels were 20-30 feet higher than they are now too. Each interglacial period is a bit different than others because the conditions that bring them on aren't exactly the same each time. I think it's difficult to ascribe warmth during Roman times or the MWP to orbital forcing (Milankovitch Cycles) because the trend in those forcings ever since the Holocene Climatic Optimum about 8,000 years ago has been downward. During the time of the dinosaurs the CO2 levels appear to have been around 1000 ppm. That alone would be enough to make it considerably warmer then than it is now. As the Earth transitions from a glacial period to an interglacial period the CO2 level rises (from around 180 ppm to around 280 ppm) primarily from the oceans outgassing CO2 as they warm up but I think also releasing some CO2 trapped in the continental ice sheets. This increase in CO2 adds to the weak forcing from changes in orbital cycles producing the full effect of an interglacial. The interglacials would never get as warm as they are without the added impetus from CO2. Natural gas is merely a stopgap on the way to zero net emissions of CO2. Anything less than that isn't going to work to stop global warming. Regarding CO2 versus natural processes, didn't Dr. Cobb explicitly state that CO2 is warming the planet? No equivocation there that I can see. Climate models are far from perfect but they're better than anything else we have (including thrown dice) and they continue to be improved by the work of people like Dr. Cobb.