02/21/2007 05:22 pm ET | Updated May 25, 2011

Teeter Totters and Tipping Points

All the teeter-totters are gone. They have been pulled from playgrounds across the country, and replaced with damped down versions that are restrained by large springs and bounce gently, never hitting the ground. Most of today's children don't know the great rush of
going over the tipping point and swinging wildly into the air, or landing with a jolt on the rocky ground.

Truthfully, the old ones always scared me as a child. A sudden dismount of your partner could send you flying down with a teeth-cracking crash onto the hard earth. And they have been banished from parks precisely because children get hurt when the tipping happens so violently. But what's been troubling me about teeter-totters lately is not their absence from parks, but the connection they have to global warming.

The thrill and danger of a teeter-totter is based on it having a
sensitive balance point. This spot, or tipping point, has many
analogies in science and culture. It is that dramatic moment when
something seems to happen all at once. Not slowly and steadily, like
knitting a sweater, but quickly and unexpectedly, like the breaching of
a dam. According to Malcolm Gladwell, author of the book The Tipping
, these tipping point moments can behave in very unusual and
counterintuitive ways.

It doesn't make sense that one tiny additional shift in the earth's
climate could cause it to tip, out of control, toward a changed world,
where all living things would be affected and many would perish. Huge
coastal population centers flooded, global weather patterns wildly
disrupted, floods, droughts, hurricanes and wildfires more severe and
deadly. At least half of the planet's species threatened with
extinction. But that is exactly what James Hansen, NASA's top climate
scientist, is suggesting.

Hansen built his first global climate model in the late 1970s, and he
is one of the world's leading authorities on climate model research.
Although we've never met, I've followed his work and we've exchanged
emails. I get the sense he's a cautious person and an exacting
scientist. My favorite story about Hansen is that when asked what he
does to relax, he answered that he likes to mow his lawn. So in 2006,
after nearly 30 years of work striving to better understand the earth's
climate, when Hansen began publicly discussing an approaching climate
tipping point on earth, it could hardly have come from a more highly
credible source. But somehow, when the news is this shocking, it takes
a while to sink in. The problem is, we don't have the time for that.

Hansen believes we are fast approaching a point of no return. He
estimates that we may have about 10 years to reverse worldwide
greenhouse gas emission trends before the climate will pass a tipping
point, and disastrously large global warming will be essentially

A huge challenge in predicting global climate change is that many
systems interact - oceans, polar ice, permafrost, cloud cover, to name
just a few. Climate skeptics, many funded by energy companies, have
tried to argue that this complexity makes conclusions about global
warming unreliable. In reality, the science is incredibly strong and
the understanding scientists now have about our global climate is
something to be proud of. In the early 1980s, before many refinements
of climate models, Hansen predicted with breathtaking accuracy the
amount of warming we would see by 2000 (1 degree F, or 0.6 degree C).
Since then, hundreds of climate scientists have worked diligently to
develop and refine our understanding of global climate, and models are
constantly improving. As a result, the major climate "forcings" -
changes in the radiation balance initiated by human activities - are
much better understood. If Hansen's conclusion is that we have about
10 years to level off and then start reducing emissions before the
earth's climate "tips," I hope he's wrong, but I'm betting he's right.
Human activities have raised atmospheric CO2 concentrations from about
317 to 380 parts per million (ppm) in the past 50 years. Hansen
estimates than if we pass 450 ppm, the earth's climate will spiral out
of control.

Hansen's conclusions are based partly on a number of systems that
scientists now understand have positive feedback loops. For example,
as polar ice caps melt, white surface area is lost that reflects heat
back into space and dark water or land surface area is added, which
absorbs heat, increasing warming. Another dramatic cause of climate
feedback is locked in frozen ground -- the melting of permafrost in
Alaska and Siberia. Trapped in the permafrost are vast amounts of
methane and other hydrocarbons, powerful greenhouse gases. As the
climate warms, permafrost melts, releasing methane, which speeds
warming. As you may have read, polar ice sheets are collapsing
rapidly, and permafrost is beginning to melt across large areas in the
far north.

If we care enough about the safety of a small number of children to
remove teeter-totters from parks, why can't we care about all
children's future safety enough to gather the will to stop the tipping
of the earth's climate?

The current impacts of climate change are tiny in comparison to what is
predicted. In Hansen's words, business-as-usual will result in a
different planet. Sea level rise will put vast, densely populated
coastal areas worldwide underwater, a catastrophic change for hundreds
of millions of people in China, Bangladesh, India, Egypt, the US, and
Europe. Species we love and depend on everywhere will face possible
extinction, perhaps half of all existing life forms. Our richest
farmlands will face severe problems with water supply, drought, floods,
and storms, causing famines and posing massive threats to global food
supplies. And catastrophic weather events, including hurricanes,
droughts, heat waves, fires, and floods will occur with increasing
frequency and severity, killing and displacing those in their paths.

If we don't curb greenhouse emissions, when will the massive changes
occur? In Hansen's words, the problems are non-linear, so it is highly
uncertain. He would not be surprised to see rapid change within 50
years. Larry King says no one cares what happens in 50 years. But I

In fifty years, my daughter will be 57, and any grandchildren I may
have will just be starting out on their own.

Those once called climate alarmists, unfortunately, seem to have
science on their side. Adaptation is a pointless concept in the face
of change of this scale. If Hansen is right, we, meaning all the
world's countries, need to act fast. Very fast. And there is some
possibility that we will.

Before we do, we have to believe in the reality of what our best
climate scientists are telling us. And this is not easy. If you are
tempted to ignore this devastating news, think of all the living things
that are depending on you to pay attention, including your children.

One decade is all we have. I believe, as Hansen does, that the best
hope is that the public must get informed and get active. We need a
tipping point in public knowledge and action. This means us. Write a
letter to the editor. Show Al Gore's movie to friends. Change your
driving, eating, and heating habits. Contact your legislators in
support of laws to first cap and then reduce greenhouse gas emissions,
promote renewable energy and energy efficiency, and develop alternative
fuels. I have never been more sure that time is of the essence. And
its not on our side.