How to stop doubting and love the climate models

A simple question, no? It's been settled with a ringing "yes" among the scientific community. Yet, the so-called "climate debate" still pops up on editorial pages, political blogs and television talk shows. Apparently, we scientists have failed to explain to the entire public how we have come to understand the climate system. For this we owe another attempt to engage readers who still feel there is some doubt about the role of human activity in Earth's climate.

What follows is a no-frills, nonpartisan explanation of how a group of scientists working on a particular problem establish knowledge, what we know, and what we need to learn.

Understanding the underlying science is important, and not just because our elected leaders in Congress are debating policy options to combat global warming, including a cap-and-trade program aimed at reducing greenhouse gas emissions. It's also important that we move the discussion to what we should be arguing about -- how to mitigate the effects of global warming -- once we get beyond the distraction of false debates over whether climate change is real and caused by humans.

A good place to begin: On Saturday, the International Day of Climate Action will feature rallies and activities around the globe in an attempt to build momentum toward the U.N. Climate Negotiations in Copenhagen in December. See www.350oregon.org for a list of activities around Oregon.

And, Nov. 18, Al Gore, winner of the 2007 Nobel Peace Prize along with the U.N.'s Intergovernmental Panel on Climate Change, will speak at Keller Auditorium as part of the Portland Arts and Lectures Series.

How do scientists establish consensus, and what is the role of consensus documents like the IPCC reports?

The complexity of the climate system dictates that the details of its function are investigated by a large, interdisciplinary community of scientists, spanning fields from geology, hydrology and plant biology, to atmospheric dynamics and chemistry. The big picture comes into focus only when combining the results of specialists in each discipline, synthesizing an enormous body of scientific literature. The scale of this endeavor makes the establishment of consensus critical to the progress of science. We select an interdisciplinary team to periodically dedicate themselves to the review of the state of climate science.

Supported by the United Nations, the Intergovernmental Panel on Climate Change Working Group I conducts a thorough review of the peer-reviewed scientific literature on climate change science. This group is made up of experts in the various subfields of climate science, whose careers are built on their reputations as careful scientists. Their authorship amounts to further staking their reputation on the conclusions, encouraging the thoroughness and appropriate scientific skepticism of the review. These consensus documents provide an internationally recognized assessment of what we know, but also, very importantly, help guide the science forward by clearly stating where the greatest uncertainties remain.

Once the progression of research, scientific publication and peer review has arrived at an explanation of individual atmospheric processes, such as cloud formation, we need a testable framework for understanding the massively interconnected climate system. For this, we develop computational climate models. Multiple research groups around the world have independently developed such models, providing an excellent means of testing their accuracy: If 12 independently written computer models roughly agree on a prediction, it is highly unlikely to be due to a random error. Models are tested by running "hindcasts" (as opposed to forecasts) to determine their skill at predicting known past trends, from the well-measured 20th century climate to the ice ages. The evidence we have that human-induced emissions have contributed to the observed temperature increase over the 20th century is shown in the graphs below.

A set of climate models from research groups around the world was run with and without human-induced carbon dioxide emissions. The model results have some spread, corresponding to remaining uncertainties in the details of the climate system. However, the observed temperature trend only falls within the model range when the human contribution is included. Scientific progress occurs when observations (temperature increase) can be explained by a physical model (human-enhanced greenhouse effect). This is the same way that we understand gravity: I can't accurately predict how rapidly an object will accelerate towards the Earth without a model that incorporates the mass of the Earth.

The global average surface temperature has increased by about 1.8 degrees Fahrenheit since 1850, with most of the increase since 1950. This warming can only be explained when including human contributions to atmospheric carbon dioxide (CO2 ). Before the Industrial Revolution, CO2 concentrations were less than 280 parts per million (ppm) for at least 1 million years; current atmospheric concentration is 385 ppm. Volcanic eruptions cause temporary cooling because of the particle haze they emit into the upper atmosphere; similarly, pollution emissions of particles from human activity have offset some CO2 warming over the past century, although the extent of this offset remains highly uncertain.

Warming is evident in other indicators as well, including rising sea level and decreasing polar sea ice and glaciers. Because CO2 remains in the atmosphere for centuries, and because oceans can store enormous amounts of heat, warming would continue for centuries even if emissions were to instantly cease.

Here's what we should be arguing about: What level of CO2 in the atmosphere is safe? The specter of accelerating climate change and the possibility of crossing a tipping point are causing heightened concern among scientists. Doubling of pre-industrial CO2 levels (550 ppm) is one oft-cited target, for which average global temperatures are predicted to increase by 5.4 degrees Fahrenheit. In contrast, some climate scientists promote aiming to preserve conditions similar to those under which life on Earth developed, which would require reducing CO2 levels from the current level of 385 ppm to 350 ppm. These alternatives would require massively different carbon policy choices, and we must decide as a public how much risk we are prepared to take.

Is "geo-engineering" an option? A few governments around the world have recently begun discussing the possibility of offsetting global warming by introducing additional reflective particles into the atmosphere, to reduce sunlight reaching the surface. At what point do we become sufficiently concerned about crossing tipping points that we should seriously consider this as a stopgap measure? Almost no research has been conducted on geo-engineering, and many disconcerting open questions remain: Will the UV-protecting ozone layer be damaged, as it is after volcanic eruptions inject natural particles into the upper atmosphere? How far will the particles disperse, and how long will they remain aloft? How will plant life respond to diminished and more diffuse sunlight? If we wish to seriously consider such action as a "bridging" strategy while we work to reduce atmospheric CO2 to a safe level, urgent research is required to understand the consequences.

The ultimate question is, how do we get there from here? Once we define target CO2 , we must begin the difficult discussions of how to get there in a way that is globally equitable and cost-effective. This is the grand challenge, and one scientists are not equipped to address. We simply advocate for moving the "debate" from false distractions to the realm of finding solutions. We're all on this little spaceship called Earth together.

Juliane Fry has a Ph.D. in atmospheric chemistry from California Institute of Technology. She teaches chemistry at Reed College.

This warming can only be explained when including human contributions to atmospheric carbon dioxide

Wouldn't it be fun to see her pony up $1000 to any of her students that could, by any stretch of the imagination, find ANY other POSSIBLE explanation.

If I sent a kid to that college, I might want some money back...

This warming can only be explained when including human contributions to atmospheric carbon dioxide (CO2 ).

I think proper grammar requires the use of "may" or "must" rather than "can" when indicating the permission or mandate of a higher authority, especially government.

Climatologists require government money to do research, or else they can only buy two thermometers and a barometer out of their own money. No government money = no research = no publication and promotions = academic poverty and being laughed at by all the climatologists with multi-million dollar research grants to prove that Antarctica will melt and Penguins will catch on fire by April.

Before the Industrial Revolution, CO2 concentrations were less than 280 parts per million (ppm) for at least 1 million years; current atmospheric concentration is 385 ppm.

I am in calculus 2215 this semester at UNCC. The mathematical model given on pg. 78 in the textbook describes the Keeling curve (function used to predict global warming by estimating the quantity of CO₂ in the atmosphere at time t years after 1950):

A(t) = 0.010716t² + 0.8212t + 313.4

The graph of this function appears as a positive region parabola curve with upward concavity (typical quadratic function graph). This mathematical model predicts 387 C0₂ ppm in the atmosphere in 2010 so it is almost as though she is simply using the Keeling curve and sounding haughty about it.

This model does not factor in solar activity, nor does it factor in volcanic activity. I want to see these computer models. I want to see the calculus they are using. I want to see the source code. They think they are so smart, so they attempt to baffle us with bs. Show us the math Miss PhD.

I do not think the "math" is know to the detail necessary to accurately explain the interaction between the Earth and the Solar as it pertains to the Earth's climate. And since the Sun is the primary driver of climate on Earth, until that relationship is known in detail, nothing is known, it's all guesswork.

And since the Sun is the primary driver of climate on Earth, until that relationship is known in detail, nothing is known, it's all guesswork.

Awww... Don't be so mean.

Just learn to LOVE the models, and all will be well!

Their graph:

Question for ya, doc... now I ain't all sceincetifical like you smart people, but why does your graph stop at the year 2000? Wasn't that about the same time that the current cooling trend started?

You are careful to note the dates of volcanic eruptions that account for earlier cooling in your models.... did I miss the eruption in 1998 that caused the current trend?

I notice that your model does not track the warming that occured in the late 30's and early 40's. What caused that?

and one more thing...

Warming is evident in other indicators as well, including rising sea level and decreasing polar sea ice and glaciers.

So if those indicateors do not track with your predictions, does that mean that your models are necessarily wrong? or are they due to:

The model results have some spread, corresponding to remaining uncertainties in the details of the climate system.

Exactly what are those "uncertianties"?

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