Beware the hockey stick

The evidence that global climate change is real and accelerating received a boost last week with publication of a new study that shows world temperatures are warmer than at any time in at least 4,000 years.

More alarming still, the findings suggest that warming will continue and temperatures are likely to surpass levels not seen on the planet since the beginning of the last ice age. Naysayers will question the data and continue their hunt for flaws in the methodology, but the conclusions are nearly inescapable.

The earth’s climate is changing, and we must take action now to try to halt the process — if it is not already too late.

Data from the last 1,500 years has shown that after 1,400 years of relative stability, global temperatures have sharply increased since 1900. Graphically, the results look like a hockey stick — a fairly flat line (representing those 1,400 years) that shoots vertically upward at the turn of the century.

Climate scientists attribute the change to human activity, in particular the increase in the use of fossil fuels as the world industrialized. New research by a team of scientists at Oregon State University has discovered that the trend is in fact more alarming and the pace of change more abrupt than originally thought.

Since thermometers have only been in use to measure outside temperature for about three centuries, scientists have had to use “climate proxies,” or natural recorders of temperature change.

Previous long-term studies mostly relied on tree rings. Since tree growth in high latitudes is mostly controlled by temperature — thick rings mean warm years — scientists had a fairly reliable indicator of temperature from periods before the use of thermometers.

But trees live only a few hundred or thousand years at most, limiting most studies to a millennium or two. The Oregon State team took samples from 73 locations around the world and used eight “climate proxies,” such as fossils in sediment on the sea floor, fossilized pollen on land and ice cores in addition to tree rings.

The researchers can now look back about 12,000 years over an entire planetary epoch called the Holocene. The Holocene began when the Earth’s orbit shifted — a natural occurrence given periodic planetary wobbles — and more incoming sunshine triggered melting at the ice caps.

The climate stabilized after about 2,000 years at a moderate level that allowed the rise of human civilization by permitting food cultivation.

For the last 5,000 years, a gradual cooling trend has prevailed, with global temperatures declining about 0.7 degrees Celsius in total. In fact, most scientists believe that if current trends continue, the Northern Hemisphere will likely encounter another ice age in a few thousand years.

Some might applaud the reversal of that trend, even though the next ice age is still several millennia away. But the change is too abrupt. Scientists believe that even if the change projected for this century is only at the mild end of the estimates, it will still warm this planet to the highest levels ever reached during the Holocene.

With temperatures during the first decade of this century warmer than at least 72 percent of the Holocene, the more realistic predictions are that it will be much worse.

Mr. Shaun Marcott, the lead researcher, believes that “By the year 2100, we will be beyond anything human society has ever experienced.”

Doubters persist. Some question whether the time between data points — 160 years — is too long a gap and could hide temperature spikes. The researchers say they have sufficient information to identify such trends if they occurred.

Other skeptics argue that global warming is part of a long-term natural trend; the Earth’s temperature is variable and this is just one end of the warming cycle.

The research shows just the opposite: If mankind had not interfered, global temperatures would still be dropping and the Earth would be reaching the end of a several thousand year cooling period. Instead, temperatures are on the rise — sharply so.

The new data show that the temperature spike in the last century is equivalent to the most abrupt changes over a 10,000-year period. That makes the change of the last 100 years even more alarming because it is even more of a departure from the norm.

Even more disturbing is the prospect of heading into new territory. Scientists are worried that the pace of change is cumulative like the speed of a ball rolling downhill — constantly accelerating.

As Mr. Marcott warned, “the rate of change is much greater than anything we’ve seen in the whole Holocene.” Most climate warming models forecast an increase of 2 to 11.5 degrees, which would have a huge impact on the planet and the people who live on it.

Later this year, the International Panel on Climate Change will release its next report on global warming. The evidence is mounting that temperatures are changing and mankind is the cause. We are beginning to see the actual impact of those changes. We are running out of excuses for inaction.