Eideard

Global temperatures are warmer than at any time in at least 4,000 years, scientists reported Thursday, and over the coming decades are likely to surpass levels not seen on the planet since before the last ice age.

Previous research had extended back roughly 1,500 years, and suggested that the rapid temperature spike of the past century, believed to be a consequence of human activity, exceeded any warming episode during those years. The new work confirms that result while suggesting the modern warming is unique over a longer period.

Even if the temperature increase from human activity that is projected for later this century comes out on the low end of estimates, scientists said, the planet will be at least as warm as it was during the warmest periods of the modern geological era, known as the Holocene, and probably warmer than that…

In the new research…Shaun Marcott, an earth scientist at Oregon State University, and his colleagues compiled the most meticulous reconstruction yet of global temperatures over the past 11,300 years, virtually the entire Holocene. They used indicators like the distribution of microscopic, temperature-sensitive ocean creatures to determine past climate…

Though the paper is the most complete reconstruction of global temperature, it is roughly consistent with previous work on a regional scale…

Scientists say that if natural factors were still governing the climate, the Northern Hemisphere would probably be destined to freeze over again in several thousand years. “We were on this downward slope, presumably going back toward another ice age,” Dr. Marcott said.

Instead, scientists believe the enormous increase in greenhouse gases caused by industrialization will almost certainly prevent that…

The modern rise that has recreated the temperatures of 5,000 years ago is occurring at an exceedingly rapid clip on a geological time scale, appearing in graphs in the new paper as a sharp vertical spike. If the rise continues apace, early Holocene temperatures are likely to be surpassed within this century, Dr. Marcott said.

Dr. Michael Mann pointed out that the early Holocene temperature increase was almost certainly slow, giving plants and creatures time to adjust. But he said the modern spike would probably threaten the survival of many species, in addition to putting severe stresses on human civilization.

“We and other living things can adapt to slower changes,” Dr. Mann said. “It’s the unprecedented speed with which we’re changing the climate that is so worrisome.”

The science is clear. It has been for a while, now. I first engaged in this debate over a decade ago and it only took me a couple of years of examining research – mostly from the Max Planck Institute – to come to conclusions requiring a commitment to action.

Responsibility still accrues to those who recognize the need to act.