In the rush to portray the perils of climate change, many other serious issues have been largely ignored. Climate change has become the poster child of environmental crises, complete with its own celebrities and campaigners. But is it so serious that we can afford to overlook the rise of infectious disease, the collapse of fisheries, the ongoing loss of forests and biodiversity, and the depletion of global water supplies?Although I'm a climate scientist by training, I worry about this collective fixation on global warming as the mother of all environmental problems. Learning from the research my colleagues and I have done over the past decade, I fear we are neglecting another, equally inconvenient truth: that we now face a global crisis in land use and agriculture that could undermine the health, security, and sustainability of our civilization.Our use of land, particularly for agriculture, is absolutely essential to the success of the human race. We depend on agriculture to supply us with food, feed, fiber, and, increasingly, biofuels. Without a highly efficient, productive, and resilient agricultural system, our society would collapse almost overnight. But we are demanding more and more from our global agricultural systems, pushing them to their very limits. Continued population growth (adding more than 70 million people to the world every year), changing dietary preferences (including more meat and dairy consumption), rising energy prices, and increasing needs for bioenergy sources are putting tremendous pressure on the world's resources. And, if we want any hope of keeping up with these demands, we'll need to double, perhaps triple, the agricultural production of the planet in the next 30 to 40 years.Meeting these huge new agricultural demands will be one of the greatest challenges of the 21st century. At present, it is completely unclear how (and if) we can do it.If this wasn't enough, we must also address the massive environmental impacts of our current agricultural practices, which new evidence indicates rival the impacts of climate change. Consider the following.Already, we have cleared or converted more than 35 percent of the earth's ice-free land surface for agriculture, whether for croplands, pastures or rangelands. In fact, the area used for agriculture is nearly 60 times larger than the area of all of the world's cities and suburbs. Since the last ice age, nothing has been more disruptive to the planet's ecosystems than agriculture. What will happen to our remaining ecosystems, including tropical rainforests, if we need to double or triple world agricultural production, while simultaneously coping with climate change?Freshwater decline. Across the globe, we already use a staggering 4,000 cubic kilometers of water per year, withdrawn from our streams, rivers, lakes and aquifers. Of this, 70 percent is used for irrigation, the single biggest use of water, by far, on the globe. As a result, many large rivers have greatly reduced flows and some routinely dry up. Just look at the Aral Sea, now turned to desert, or the mighty Colorado River, which no longer sends any water to the ocean, for living proof. And the extraction of water from deep groundwater reserves is