I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.
By: Dr. Ricky Rood , 18:38 GMT le 03 août 2011
Is this year what we can expect?
In recent weeks a question I have been asked often, “is this year, the last couple of years, like what we can expect in the future?” The question is often asked quietly, perhaps by a planner, say, someone worried about water in their city. The question follows from not only a perception that the weather is getting “weird,”, but also some small aspect of experience in their job. For example, a water manager recently said they were seeing their local river showing a distinct change to sporadically high flow in the winter, smaller spring flows, and extremely small flow late in the summer. Is this what I should expect in the future? The short answer is yes.
This question of expectation has rolled around in my head for years. I am a gardener with aspirations for small farmer. Over the last 30 years, I have definitely pushed my planting earlier in the year. When I was in Maryland, I felt wet, cool Mays were becoming the “norm,” with my tomatoes sitting in sodden soil. At the same time I would recall plots I had seen in some recent presentation that showed modeled shifts in the warm-cold patterns suggesting springtime cooling in northeastern North America. These are the sorts of casual correlations that lead people to think are we seeing a new “normal.”
In 2008 I wrote a blog about the changes in the hardiness zones that are reported on the back of seed packages. These are the maps that tell us the last frost date, and there were big changes between 1990 and 2006. These changes in the seed packets caught the attention of a lot of people. Recently, NOAA published the “new normal.” This normal relies on the definition of climate as a 30 year average. (AMS Glossary) What was done - at the completion of the decade NOAA recalculated a 30 year average. That is, 1981-2010 rather than 1971-2000. This average changed a lot, with notable warming of nighttime minima. There was some regional reduction of summertime maxima; that is, cooling. All in all, the average temperature went up, with most of the increase in nighttime minimum, a fact that is consistent with both model simulations and fundamental physics. This also came with another update of those hardiness zones.
When trying to interpret climate information and determining how has climate changed and how will it change, the combination of observations, fundamental physics, and models provide three sources of information. The combination of this information and the determination of the quality of that information is subject to interpretation. In the case of determining whether or not we are already experiencing the climate of warming world and how that change will be realized in the next decades it depends on how we use the models.
In my previous entry on heat waves, I implied how to use these pieces of information together. There are fundamental physics in the relationship between temperature and moisture in the air; hot air holds more water; warm water evaporates more quickly. The question of the model is - how well does the model represent the movement of that moisture? For the heat wave example, it is important how well do the models represent persistent high pressure systems over North America in the summer? Are these high pressure systems represented well by the models for the right reasons? The answer to the model question has a range of answers. The model does represent these systems, but if you are an expert in summertime persistent high pressure systems, then you can provide a long list of inadequacies. How can we glean information about the quality of the model? If we look at weather models, then we were able to predict the heat wave – even with the inadequacies that the expert or skeptic can list. Returning to the climate model, do we see like events in the current climate, and do these events change as the planet warms? The answer is yes. Then can we use this to guide our development of plans to adapt to climate change? The answer is yes, if we can connect the model back to data and the fundamental physics. This does become a matter of interpretation – how strong or weak is that connection?
The more I work with planners the more I hear the need for interpretive information, expert guidance, advisories about climate and climate change. People start with the notion that they want digital data from climate models that looks like current weather data. Once presented with 1) the logistical challenges of using that data, 2) the complex nature of the uncertainties associated with that data, and 3) the relative importance of climate to other parts of their decision package – once presented with these facts, they move to the need for advice. This makes sense - most of us want a narrative weather forecast, rather than model output. And the models play the same role in the use of weather forecasts as they do in climate projection. The models guide our thinking, with the ultimate forecast based on that guidance refined by observations and fundamental physics.
This entry started with the question I hear more and more – is this year what we can expect more of in the future? I have a mantra which is that on average the surface of the Earth will warm, ice will melt, sea level will rise, and the weather will change. What we are seeing here is weather changing in a warming, more energy laden, environment. The extraordinary extremes that we have seen in the last year and are seeing this year are quite solidly connected to both fundamental physics and the guidance from climate and weather models. Hence, my answer, as I walk around my garden, thinking how to get better tomatoes next year, thinking about my irrigation system in my doddering retirement, is yes, what we are seeing this year tells me about what to expect in a future that is relevant to me - not something far off.
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