While disasters like hurricanes and floods are better remembered, heat waves cause more fatalities annually than all other natural disasters combined. Close to 800 people died in Chicago alone during a searing heat wave in 1995.

As our fossil-fuel orgy drives the earth’s temperature upward, extreme-heat events will become more common, say researchers. A study published last December in Environmental Health Perspectives concluded that, with no reduction in greenhouse-gas emissions, Chicago will experience a 1995-magnitude heat wave once every year by the last two decades of this century.

“I don’t think there’s a widespread appreciation of the health effects of climate change,” says Dan Ferber, a contributing writer to the journal Science and co-author (with the late Paul Epstein, a professor at Harvard Medical School) of the first book on the subject, Changing Planet, Changing Health, published in 2011. In addition to heat waves, humans are already suffering from climate-induced woes, says Ferber. Record amounts of pollen this spring are causing misery for allergy sufferers. Droughts are reducing global food production, increasing the likelihood of famine, particularly in the Horn of Africa. (A multi-year drought in Texas has caused $14 billion in agricultural losses so far.) More frequent forest fires are thought to be increasing the incidence of respiratory illnesses in the American West. Infectious diseases are spreading to new areas.

Take Lyme disease, a sometimes crippling infection spread by ticks. Part of the tick’s life cycle is spent on the ground. If it’s too cold, it dies. Milder winters mean more ticks are surviving—and spreading Lyme disease — farther to the north.

“The disease is already 10 times more common in Maine than it was a decade ago,” says Ferber, “and it’s moving into Canada.”

Health effects are just one new piece of the climate-change puzzle that researchers have been fitting together since the Intergovernmental Panel on Climate Change (IPCC) issued its most recent overall climate-change assessment in 2007 (the next one is due in 2014). The picture that’s emerging is worse than previously thought, with extreme events occurring more frequently and much earlier than predicted. Worse, the window of opportunity for reversing these trends appears to be closing. At a London conference in March, scientists warned that we may be reaching a tipping point.

“We can…cap temperature rise at two degrees [Celsius],” said climatologist Will Steffen, “or cross the threshold beyond which the system shifts to a much hotter state.”

This is largely due to a number of “feedback loops” — environmental conditions caused by climate change that accelerate warming.

The destruction of the Amazon rainforest is one such loop. An estimated two billion tons of carbon was released in 2010 as vast swaths of rainforest were burned to run cattle or to grow soybeans to feed them. The resulting increase in temperature is causing droughts that will lead more of the rainforest to die off, continuing a self-reinforcing cycle that will be hard to reverse.

An even larger threat is posed by the fate of Arctic permafrost — soil that typically remains frozen year round. If the permafrost thaws, as is now thought likely, 190 billion tons of carbon trapped in the permafrost could be released into the atmosphere over the next two centuries — about half the amount of carbon released by human activity since the beginning of the industrial age.

For decades, scientists have predicted a climate-induced rise in sea level. What’s new is the estimated speed of the water’s rise and how high it’s now predicted to go. In the 2007 IPCC report, the predicted sea-level rise was 15 inches by the end of this century. But that was before scientists realized that large portions of the massive ice sheets covering Greenland and Antarctica would likely melt.

Factoring in this additional water, the new estimate, based on research recently cited by U.S. Geological Survey scientist Tom Suchanek, is more than triple the old one — up to 47 inches. (Other scientists predict an even greater increase.)

Higher levels of CO2 are changing the chemistry of the ocean, turning it more acidic, which could be disastrous for shellfish, reef-building corals, and the thousands of species that depend on reefs. A paper published in the journal Science (coincidentally, just 10 days before Santorum’s ignominious statement) reported that, if we continue down the energy path we’re currently on, the ocean will become more acidic than at any point in the last 300 million years. The authors of the study warn that we are “raising the possibility that we are entering an unknown territory of marine ecosystem change.”

The phrase “entering unknown territory” sums up our global ecological outlook on a warming planet. “Climate” is a simple word for an enormously complex set of interactions involving both the living and the non-living worlds.

Over time, what were once theoretical events become reality. In 2008, for example, a team of paleobiologists warned that warming temperatures in Antarctica could allow crabs to invade and decimate a marine ecosystem that had been protected by cold water for 14 million years.

Last September, a different team used submersibles equipped with video cameras to film a colony of more than a million red king crabs, many of them over a yard across, that had established a claw-hold off the West Antarctic Peninsula, near where the first team had anticipated just such an incursion.

There are also possible consequences that only a handful of experts have imagined. In Waking the Giant, a book due out in May, leading volcanologist Bill McGuire reports that glacial melting in Alaska has already triggered earthquake activity in the region.

The mechanism is surprisingly simple, explains McGuire, a professor of geohazards at the University of London. Removing the tremendous weight of ice from the land causes existing faults in the earth’s crust to shift.

“The crust beneath the Greenland ice sheet is already rebounding in response to rapid melting,” writes McGuire. Earthquakes there could trigger underwater landslides that, he posits, could spawn “tsunamis capable of threatening North Atlantic coastlines.”

The ever-growing parade of horribles linked to climate change should provoke a demand for action, for even the gloomiest climate scientists say there is still time to avoid the worst of these scenarios — if changes are made immediately. At this point, however, it is hard to make the case for optimism. Even as the earth warms, our national political will appears frozen in ignorance, à la Santorum, and denial.
Osha Gray Davidson, author of five books of nonfiction, publishes The Phoenix Sun, a syndicated online news and analysis site covering solar power from the American Southwest.