We’ve had “global warming” for more than a decade -- the hottest decade on record worldwide. Is this the “greenhouse effect” that scientists have been warning about, i.e. a response to increased carbon dioxide in the atmosphere, or is it some natural -- not man-made -- climatic change?

The Intergovernmental Panel on Climate Change (IPCC) has cautiously proposed a “discernible” human influence. The IPCC is a cautious body not disposed toward outright conclusions. And actually most of the several climate models do not predict the sudden increases in temperature of recent years.

Something is going on. What does it tell us about the need to curtail, drastically, carbon emissions during the coming century?

The popular guessing game -- do we see a greenhouse “signature,” can we identify a clear “signal” in the “noise”? -- is probably premature. The history of climate shows that sudden changes of global atmospheric temperature have occurred. There are random or “chaotic” influences on global climate -- El Niño is an example, volcanic emissions are another. There are anthropogenic (man-made) influences besides greenhouse gases: aerosols of dust and, especially, sulfur emissions can block incoming sunlight. Urbanization can produce “heat islands” that affect temperature estimates. Finally, most of the globe is ocean; the specific heat of water is great relative to air, and the oceans act as a huge cooling reservoir that delays by perhaps decades the appearance of atmospheric warming.

So the recent temperature record is unlikely to be conclusive on the cause of the warming. Greenhouse warming is not clearly established by the temperature record, nor is it in any way ruled out. We may see the greenhouse “signal” clearly in another decade or two. Meanwhile we have to rely on what science can tell us.

Earth is unique in our solar system for its temperature range, and greenhouse gases are to be thanked. Another well-understood fact is that carbon dioxide molecules do absorb infrared radiation. Carbon dioxide is transparent to incoming sunlight; but as the earth, warmed by daylight sun, radiates energy back into space, it does so in the infrared part of the electromagnetic spectrum, and the carbon dioxide absorbs it and gets warm.

Carbon dioxide is only one of several gases that have that property. The most important one is water vapor, and part of the estimated enhancement of temperature is the positive feedback of warming on absolute global humidity.

(Incidentally, actual greenhouses do not produce the “greenhouse effect,” they merely trap the air that is warmed by contact with the ground that is warmed by the sun. We should have called it the “smudge pot effect.”)

I find the case for prospective greenhouse warming to be substantial. The uncertainties are not mainly about whether greenhouse warming is going to be real, but about the magnitude and speed of warming, about the variegated climatic effects -- not just “warming,” but all the changes in precipitation, humidity, sunlight and clouds, storms, and variations between night and day, summer and winter, polar regions and tropical, mountains and plains, east coasts and west.

In the two major unspecialized scientific journals, Science and Nature, one has to go back a decade or two to find serious doubts about the basic science. Rarely is there such scientific consensus as there is on whether the greenhouse effect is real, even though it can not yet be uncontrovertibly detected in the climate record.

But the uncertainties are daunting: the best the IPCC can do is to give us a range of possible warming for any given increase in carbon dioxide. And the upper bound of that range has been, for over 20 years, three times the lower bound! -- an enormous range of uncertainty.

On top of that are the uncertainties of what the changes in temperature will do to climates around the world.

And on top of that are the uncertainties of what those climate changes may do to the worlds we live in. And what people can do to adapt successfully.

I’d buy insurance. But I’d do it prudently, and without great alarm. Yet!