Good news: Some ecological damage is reversible. Removing large fish from coral reef ecosystems can eventually kill it, but protect a reef from fishing, and it can bounce back. Stop cutting down trees, and a forest may recover.

Climate change, on the other hand, can cause irreversible damage, says Anthony Barnosky, professor of integrative ecology at University of California-Berkeley. For example, an increasingly acidic ocean will not only kill coral, but it will keep the coral from coming back; and changes in the life cycle of pests (a likely consequence of climate change) can prevent a forest from regrowing.

The rate of species loss on earth today is at least three to 12 times higher than it has been for millions of years, Barnosky says. “What’s special about today is more change within a short time. Throughout earth’s history, we have been within a 10 degree C fluctuation,” or within 20 or so degrees Fahrenheit.

The Intergovernmental Panel on Climate Change, an international scientific body formed by the United Nations, involves thousands of scientists from around the globe. The IPCC stated in its Fourth Assessment Report, “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.”

Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years, according to the report, and likely the highest in at least the past 1,300 years.

The IPCC developed a variety of possible climate change scenarios based on varying levels of certain emissions (for those who really want to know: CO2, CH4, N20 and F gasses). “Now, under any scenario,” Barnosky says, “we will be hotter than humans have ever seen nature by 2070, if not sooner.”

During the past 100 years, the global mean atmospheric temperature has increased .74 degrees C (approximately 1 degree F on average around the globe), but high latitude areas have warmed much faster, says Virginia Van Sickle-Burkett, chief scientist, Climate and Land-Use Change at the US Geological Survey. Alaska, for example, has warmed about 3.5 degrees F since 1950, and winters in Alaska have warmed even more, by 6 degrees F since 1950.

The increase in atmospheric temperature has led to a decline in glaciers and ice sheets. The warming of the atmosphere has also increased the amount of water vapor in the atmosphere, as well as changes in patterns of rainfall, creating new dry areas while others experience record rainfall.

The temperature of our oceans is also changing; from 1961 to 2003, global ocean temperature increased down to a depth of at least 700 meters. Many scientists attribute the intensity of hurricanes and other tropical storms to rising sea surface temperature, she added and the acidity of the ocean is increasing as the oceans absorb carbon dioxide at higher rates from the atmosphere.

Van Sickle-Burkett says that other ecological consequences of climate change in the southern U.S. include higher winter temperatures; more intense droughts; lower soil moisture, resulting in more intense, widespread and frequent wildfires; coastal shoreline erosion and wetland submergence; increasing salinity in fresh and brackish water systems, affecting coastal forests; increases in invasive species; change in plant and animal distribution and phenology (essentially the timing of biological events like the leafing out of plants); and increased tidal and storm surge flooding.

In short, she says, “Our coast is falling apart.”

In addition, Van Sickle-Burkett reports, the IPCC says that the global average sea level has risen since 1961 at an average rate of 1.8 mm/yr and since 1993 at 3.1 mm/yr, and the rate of global sea level rise is expected to increase this century. A rise of 3-6 mm a year may not sound like much, but over a period of 100 years this adds up to a foot or two increase in mean sea level.

One foot of sea level rise would inundate many coastal wetlands in Texas and accelerate barrier island losses all along the Gulf Coast.

Animal species that cannot move to new habitat likely will go extinct from climate change, Barnosky warns. Those that can move may survive — but they may not find a place to go or a way to get there. About 43 percent of the earth’s land has been altered for agriculture and human habitation, and even more by our global transportation system (roads, canals, tracks, shipping lanes). As Barnosky says, “It’s hard for species to get from Point A to Point B,” even if a Point B is available.

Some species may be able to evolve, but evolution can only happen so fast. The winners here will be insects and bacteria, which can evolve much faster than other species.

Extinction happens when a species can’t tolerate changes physiologically or developmentally. Pikas are the poster child for physiology-driven extinction; they die at temperatures of 78 degrees, and could simply run out of cooler places to go. An example of development-driven extinction are oysters, which fail to grow in warmer and more acidic waters.

Then there are what Barnosky calls extinction wild cards, including seasonal mismatch, such as when animals emerge from hibernation too early and miss out on a food source. Species interactions are another. Take, for example, the removal of keystone species and coral bleaching, where, when temperatures rise beyond a normal range, coral organisms expel their symbiotic algae and may die if normal conditions don’t return quickly enough.

In a paper published June 6 in Nature, Barnosky and 21 other scientists warn that we may be fast approaching critical, planet-wide ecosystem tipping points. One we’ve already reached, he says, is oil.

“We have passed the point where oil is cheap and easy to get out of the ground and will eventually reach a point where it becomes too expensive to extract the last drops. We have about 50 years of oil left, based on 2009 consumption. So we have 50 years to phase in clean energy.”

It's due time to get started.