What does climate change portend for birds?

Birds will be stuck with the climate we are giving them, probably for thousands of years.

A friend of mine tells me he hopes to die before the worst of our new climate becomes apparent. My friend has heavy mileage, but maybe not enough.

Predictions for the growth of CO2 content in the air give me a good chance to be here for at least the overture to a truly bent climate.

My friend and I won't have to adapt to the same degree demanded of birds. Climate is starting to require changes that many animal species will find difficult or impossible.

For several years I've followed the steady increase of carbon dioxide in the atmosphere. Content was 380 parts per million (ppm) when I began. As I write on this day, in early August, 15 years later, the count is 413.93 ppm.

(A few hundred parts in a million sounds so minor. This is physics, however; small numbers can have significant meaning.)

The CO2 gain is close to two parts per year. I've read scientists' predictions that the tipping point — where the downhill slide can't be reversed — is a very pessimistic 430 ppm (that's eight years from now). Others say 450 ppm or more. Predictions vary; in any case, the trigger number is a scary unknown.

Michael Mann, professor of meteorology at Penn State University, recently said on livescience.com that CO2 levels above 450 ppm "are likely to lock in dangerous and irreversible changes in our climate."

Birds evolved to live successfully in particular climates. That's why bird species change as you move north or south. Birds in Florida are not the same birds you see in Alaska.

CO2 is critical, as you probably know, because it traps and holds heat. The more CO2 in the air, the more … well, you see the point.

The atmospheric carbon dioxide level one day in May this year was 415.39 ppm. That was noted as the highest CO2 level in at least 800,000 years.

"The most direct evidence [of historic CO2 levels] comes from tiny bubbles of ancient air trapped in the vast ice sheets of Antarctica," wrote Andrew Freedman for the website Climate Central (climatecentral.org). He currently writes about weather for the Washington Post.

Overall, it will be a long, long time before our weather is better than it is right now. It takes thousands of years for CO2 in the air to dissipate.

(Daily CO2 measurement is taken at Mount Mauna Loa Observatory in Hawaii. You can see current numbers and a history of atmospheric CO2 at co2.earth. The count fluctuates by day and season, usually by fractions of a point.)

Confronted with excessive heat, birds will reduce activity, pant as a cooling strategy, and seek shade. Like us, birds need water for cooling and to simply stay alive. High temperatures cause birds to lose water faster. They can die of heatstroke or dehydration.

Studies of past cases of excessive heat show that it causes birds to reduce the frequency with which parents feed nestlings. This impacts chick size, and survival when they fledge.

Another difficulty is that the insects essential to most feeding regimens also will seek cooler places. They become more difficult for birds to find.

Some bird species will adapt; birds already are moving territories in a northerly direction. Other species probably won't make it. And others yet will evolve tolerance, although neither my friend nor I nor you likely will live long enough to see that.

"… What was supposed to be happening 50 years from now is our present reality." — Edwin Castellanos, climate scientist, Universidad del Valle, Guatemala.

Read Jim Williams' birding blog at startribune.com/wingnut.