Simple Sam Learns What Climate Change Is & Gets Some Homework

Posted on August 18, 2010


Today in our second lesson in climate school we’ll start by discussing what is and what isn’t climate change.  Yes, Sam?

“Shouldn’t you first tell us the difference between weather and climate?”

You don’t know?

“You always go on about the difference between weather and climate,” says Sam.  “Weather is…, yadda yadda yadda.  Climate is…, yadda yadda yadda.”

Well, I thought my comments had more snap and verve than that, Sam.  But I take your point. …

Weather is not climate, as Sam wishes us to know.  Weather is day to day.  Particular. — It rained.  The airport registered a temperature of 24.  There was a wind from the west gusting to 10 knots.  Bring sunscreen to the beach on Saturday.

Climate, in contrast, is all about averages and patterns in weather.  What the usual range of temperature in summer is.  What the average temperature in winter is.  How hot does it get?  How cold does it get?  How often does it rain, and when?  The average, the extremes, the patterns of things, that’s what climate is about–if we want to generalize and simple-mind it.

“Is that a comment?” asked Simple Sam.

Didn’t intend it.  Sorry, Sam. — So when we talk about climate change, were talking about shifting these averages.  It’s hotter.  It’s colder.  It’s wetter.  It’s earlier.


Climate is complex, Sam.  A stable shift of a weather pattern could leave a particular place slightly cooler than it usually is, even though most other places are warming up.

“Sounds like you climate guys are covering all your bases.”

One of the important concepts to understand about climate, Sam, is that we’re talking about general patterns here.  It takes a whole lot of temperature and tree-ring readings to establish a general pattern in a whole planet.  It takes planetwide data and thousands of datasets.  And, just so we know what we’re looking at is for real, and not, for instance, just a particularly wide swing of the climate pendulum, we have to see whether what we’re looking at actually lasts.  Climate change doesn’t usually qualify as climate change unless it persists for decades or longer.

“But doesn’t weather just change anyway?” says Sam.

Of course it does, but when we’re talking about climate change, we’re not just talking about changes in the weather from day to day, from summer to winter, or even from year to year.  For one thing, climate is usually estimated over 30 year periods or more, just so all the fluctuations in weather caused by El Niño and La Niña, solar cycles, and other similar influences, can be accounted for and filtered out of our calculations.

You see, just because climate change has moved in doesn’t mean all the other things that influence climate have moved out.

Now when something happens like the climate of the entire earth shifts, when the average surface temperature of the planet rises, and this goes on for a long time everywhere, then climatologists say, okay, this is real, and start to look around for suspects.

What’s causing the warming?  Variations in the sun’s output?  Is the sun warmer?  (No?  Cooler you say?)  Are there recent changes in the earth’s orbit somebody forgot to tell us about?  Variations in cloudiness?  Variations in the earth’s ice cover?  Changes in greenhouse gas concentration?

“Did you just think of that last one now?” asks Sam.

Sam, I believe you are picking up a gift for sarcasm.  Did you get it from me, perhaps?  I know I’m not really your hero or …

“Could you please just continue.”

Okay, Sam.  Well, you know if you want to detect climate change on a global scale, you will need simultaneous observation on a global scale.  That wasn’t possible to do–not directly–before the second half of the nineteen century.  Indirectly, we have found ways of determining climate changes before that time by using indicators like ocean sediments, tree rings, coral reefs and ice cores, all of which are sensitive to climate in predictable ways.

“Even if there are changes, what proof do you have that it’s not just natural variation?” asks Sam.

We know all about natural variations, Sam.  I mentioned El Niño, which can warm the world for a year or so at a time, but hardly much more.  Other ocean systems also oscillate and produce climactic variation for a while.  However, nowhere in the last two thousand years is there evidence of the kind of changes we are going through now.  Never have temperatures risen so fast and so high as in the last century.

“Who says so?”

You want the science, Sam–and whole bunch of extra homework before our next lesson, if you’re so inclined—you can start by looking here:

Committee on Surface Temperature Reconstructions for the Last 2,000 Years, Board on Atmospheric Sciences and Climate, and Division on Earth and Life Studies (2006) Surface temperature reconstructions for the last 2,000 years, National Academies Press, Washington DC.

Description. In response to a request from Congress, Surface Temperature Reconstructions for the Last 2,000 Years assesses the state of scientific efforts to reconstruct surface temperature records for Earth during approximately the last 2,000 years and the implications of these efforts for our understanding of global climate change. Because widespread, reliable temperature records are available only for the last 150 years, scientists estimate temperatures in the more distant past by analyzing “proxy evidence,” which includes tree rings, corals, ocean and lake sediments, cave deposits, ice cores, boreholes, and glaciers. Starting in the late 1990s, scientists began using sophisticated methods to combine proxy evidence from many different locations in an effort to estimate surface temperature changes during the last few hundred to few thousand years. This book is an important resource in helping to understand the intricacies of global climate change.

Kaufman, D. S., Schneider, D. P., McKay, N. P., Ammann, C. M., Bradley, R. S., Briffa, K. R., Miller, G. H., Otto-Bliesner, B. L., Overpeck, J. T., Vinther, B. M., and Arctic Lakes 2k Project Members (2009) Recent warming reverses long-term Arctic cooling, Science 325, 1236–1239.

Abstract. “The temperature history of the first millennium C.E. is sparselydocumented, especially in the Arctic. We present a synthesisof decadally resolved proxy temperature records from polewardof 60°N covering the past 2000 years, which indicates thata pervasive cooling in progress 2000 years ago continued throughthe Middle Ages and into the Little Ice Age. A 2000-year transientclimate simulation with the Community Climate System Model showsthe same temperature sensitivity to changes in insolation asdoes our proxy reconstruction, supporting the inference thatthis long-term trend was caused by the steady orbitally drivenreduction in summer insolation. The cooling trend was reversedduring the 20th century, with four of the five warmest decadesof our 2000-year-long reconstruction occurring between 1950and 2000.”

Mann, M. E., Zhang, Z. H., Hughes, M. K., Bradley, R. S., Miller, S. K., Rutherford, S., and Ni, F. B. (2008) Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia, Proceedings of the National Academy of Sciences of the United States of America 105, 13252–13257.

Abstract. “Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature Reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats. The reconstructed amplitude of change over past centuries is greater than hitherto reported, with somewhat greater Medieval warmth in the Northern Hemisphere, albeit still not reaching recent levels.”

Posted in: Climate School