Imagine for a minute that global warming is not changing our planet's biosphere and the ecosystems that sustain life on Earth.

Imagine that climate change abetted by rising human-generated emissions of greenhouse gases does not threaten freshwater supplies, agriculture, marine ecosystems, human health, coastal settlements and the very existence of small island states.

Imagine climate changes are not likely to trigger mass migrations and state conflicts, as growing populations of landless, hungry and thirsty people scramble to grab portions of the shrinking global pie.

If this were true, would there still be any reason for our leaders to gather in Copenhagen next month and agree on concrete plans for reducing greenhouse-gas (GHG) emissions, such as of carbon dioxide, methane, nitrous oxide and fluorocarbons?

The short but emphatic answer is "Yes."

According to recent research, climate is just one of at least nine critical biophysical parameters that are essential for Earth to maintain its capacity for self-regulation, and for humans to remain within these limits will require the very best international cooperation we can muster.

Which is why getting it right in Copenhagen is so important.

Substantial progress in December will give us a blueprint for dealing with climate and for dealing with each of the other biophysical limits we are going to bump up against in coming decades.

Yet, with the conference in Denmark just weeks away, some commentators have already chosen to declare the talks a failure. This knee-jerk pessimism is unfortunate, because it encourages low expectations at a time when policymakers and negotiators should be redoubling their efforts to craft a comprehensive and effective treaty.

There is no denying that complex and very real obstacles stand in the way of international cooperation on climate change: Opinions among developing and developed countries differ greatly on who should take responsibility for the phonomenon, and how; there are fears that efforts to reduce GHGs will trip up already limping economies; and, there is considerable disagreement over how best to measure and reduce emissions.

Nevertheless, international cooperation remains key for dealing successfully with global environmental challenges, and Copenhagen offers a chance to step boldly beyond 1997's Kyoto Protocol to the United Nations Framework Convention on Climate Change, which was finally ratified in November 2004.

Critics of global climate negotiations predictably argue that the Kyoto Protocol did not successfully curb GHG emissions, with few countries achieving their reductions and many, including Japan, allowing emissions to climb.

But despite its shortcomings, Kyoto did succeed in galvanizing global awareness, creating various mechanisms for nations to cooperate in reducing GHGs, and building international momentum toward the Copenhagen talks.

Copenhagen, too, can already be considered a success in some respects.

"In a short span, many nations have pledged to cut their emissions of greenhouse gases by considerable amounts, well beyond any commitments they had made before," notes a commentary appearing last month in Nature magazine (Oct. 22). "Norway, for example, offered this month to reduce its own emissions by 40 percent below 1990 levels by 2020. Indonesia said it would curb its emissions over that same time by 26 percent below the levels expected under a business-as-usual scenario, with even stronger cuts possible under an international agreement. The European Union has committed to a 20 percent reduction below 1990 levels and would increase that to 30 percent with a global pact. And, for the first time," the commentary continues, "the U.S. Congress is moving towards establishing laws that mandate emissions cuts."

As Nature points out, though, promises are not achievements. Nevertheless, "they at least show that countries have started to analyse their own emissions seriously and to develop domestic agendas that would set them on course to meet their commitments. Such unilateral decisions are an essential starting point for an international agreement, and they suggest that countries are now ready to back up their rhetoric in a way that was not true 12 years ago, when they signed the Kyoto Protocol. This is real progress, and it would not have happened without the pressure to produce a treaty," states Nature.

Which is good news, because human society is going to need all the cooperation and commitment it can muster in coming decades as human populations undermine other biophysical thresholds and threaten Earth's ability to provide for human life.

In Sweden, a team of Earth-system and environmental scientists led by Johan Rockstrom of the Stockholm Resilience Centre has already begun research "to define the boundaries of the biophysical processes that determine the Earth's capacity for self-regulation," a feature article in the September issue of Nature reported.

The scientists there are attempting to take a holistic look at planetary systems and how human demands on these systems are putting stress on the entire planet, states the article, titled "A Safe Operating Space for Humanity."

"We have tried to identify the Earth-system processes and associated thresholds which, if crossed, could generate unacceptable environmental change. We have found nine such processes for which we believe it is necessary to define planetary boundaries: climate change; rate of biodiversity loss (terrestrial and marine); interference with the nitrogen and phosphorus cycles; stratospheric ozone depletion; ocean acidification; global freshwater use; change in land use; chemical pollution; and atmospheric aerosol loading," explain the authors.

The boundaries for three systems — climate change, rate of biodiversity loss, and human interference with the nitrogen cycle — have already been overstepped with unknown consequences for the environment and human society, warn the scientists.

For the past 10,000 years, Earth's environment has remained remarkably stable, with regular temperatures, freshwater availability, and biogeochemical flows fluctuating within narrow ranges. This period, known as the Holocene, has now been replaced by the Anthropocene, during which human activities have become primary sources of global environmental change.

"Now, largely because of a rapidly growing reliance on fossil fuels and industrialized forms of agriculture, human activities have reached a level that could damage the systems that keep Earth in the desirable Holocene state," explain the authors. "The result could be irreversible and, in some cases, cause abrupt environmental change, leading to a state less conducive to human development."

Not surprisingly, this process of identifying systems and thresholds requires many qualifications. The values chosen as boundaries by Rockstrom's team are for the most part arbitrary, the boundaries do not always apply globally as local circumstances often differ, and "assigning 'acceptable' limits to processes that ultimately determine our own survival is risky as some of the suggested limits may be easier to balance with ethical and economic issues than others," note Nature's editors.

Nevertheless, the challenge is an essential one in much the same way carbon footprinting is: It helps to calculate, and respond to, the demands that production, consumption and wastes put on local, regional and global ecosystems.

With a better understanding of how Earth's biophysical systems work, we can better craft land use, resource use, agriculture and emissions policies, both nationally and internationally.

"The evidence so far suggests that, as long as the thresholds are not crossed, humanity has the freedom to pursue long-term social and economic development," conclude the authors.

The danger, of course, is that in our eagerness to grow our economies and exploit Earth's bounty, we will push our planet beyond these thresholds — compromising the life quality of our children and grandchildren.

For better and worse, risk-taking is in our genes. We often push to the limit and when we do we win or lose big. So far we have taken the big payouts, leaving the losses to future generations.

The very least those generations now deserve is a push to the limit in Copenhagen.

Stephen Hesse can be reached at [email protected]