Yep, Nelly, that cow’s left the barn.
You can choose not to believe in climate change, but it's pretty much a done deal. A landmark peer-reviewed study (Cook, et al., 2013) evaluated 10,306 scientists, and concluded that over 97 percent of climate scientists agree that global warming is real and largely caused by humans. These are the guys actually gathering the data and doing the scientific analyses – not politicians. No “belief” is really necessary anymore, because evidence such as spiking carbon dioxide in the atmosphere, sea-level rise, the disappearance of arctic sea-ice, northward migrations of pests, and decimations of formerly healthy species are all around us.
In fact, climate change has been going on since the beginning of time, and there is a huge trove of geologic evidence supporting the fact that our world is always changing. This evidence comes from stable isotopes in lake sediments. It also comes from fossil evidence such as cold-blooded fresh water animals whose remains have been found in Antarctica. It comes from packrat middens (ancient packrat nests that can be dated using Carbon-14) and tree-rings (Thompson, 1990). One of us has visited Anasazi building sites in the southwestern United States, and the density of these structures in now-waterless lands prove that a large number of people lived in a region that today could no longer support even a fraction of that evident population. We could fill our house with all the documentary evidence that has been accumulating that shows our climate has changed and is changing.
What climate-change deniers are fighting about most about these days is a slightly more specific question: how much of the recent climate change is Anthropogenic – that is, caused by humans? It's no surprise to anyone that we are using more fossil fuels today than are being replenished, by many orders of magnitude. Records kept since the 1950's at an atmospheric observatory on Mauna Loa volcano's north flank in Hawai'i show a steady rise in CO2 in our atmosphere. It has gone from 312 parts per million in 1955 to over 400 ppm today. (See for instance http://www.esrl.noaa.gov/gmd/ccgg/trends/ ).
That’s a 25 percent increase of carbon dioxide in the atmosphere in less than our lifetime!
Recently, scientists have made enough measurements to quantify what is contributing to this CO2 increase in our atmosphere. It’s not volcanic eruptions. A USGS scientist named Terry Gerlach (Gerlach, 2011) showed that volcanoes do not contribute most of the CO2 to our atmosphere. In fact, they contribute a minuscule amount, two orders of magnitude less than the contributions to atmospheric CO2 from humans. Here are the final measured numbers:
Volcanoes: 0.26 Gigatons of CO2 per year
Humans: 35.00 Gigatons of CO2 per year
And it's accelerating: there has been a 550 percent increase in the rate of atmospheric CO2 emissions just since 1950. CO2 is a known greenhouse gas, as high-school kids sometimes prove in physics classes. A greenhouse gas is a gas that causes heat to be retained by our atmosphere. Methane is an even more effective heat-retaining greenhouse gas than CO2 – and the dramatic increase in population in the past century of people who want to eat beef has dramatically raised the methane naturally released by herbivores in their fermentation-digestion process.
How could the CO2 emission rate ramp up so strongly? Well, for starts, China is bringing one new coal-fired power plant online nearly every week. There are commonly dense-smog days that are declared health hazards by the American embassy, because the Chinese government has blocked publication of the air-quality numbers. India is fast converting itself from a rural agrarian society to a society of middle-class people who ALL want their own car. While some American states and European countries are making small steps, they are nowhere near enough to offset the huge carbon and particulate emissions from just these two countries alone.
There is now even a new name for this era we live in: the Anthropocene. Until recently, geologists broke up prehistory into several categories:
The Precambrian Era ended about 542 million years ago (we start seeing fossils).
The Paleozoic Era ended about 250 million years ago – when 95 percent of all living things died during what is called the Permian Extinction.
The Mesozoic Era (the age of Dinosaurs), which ended about 65 million years ago when a 10-km/6-mile diameter asteroid crashed into what is now the Yucatan Peninsula.
We are now in the Cenozoic Era, which has several sub-sets:
- The Paleocene lasted until 56 million years ago
- The Eocene (when horse ancestors first appeared) lasted until 34 million years ago
- The Oligocene lasted until 23 million years ago
- The Miocene lasted until about 5 million years ago
- The Pliocene lasted until about 1.8 million years ago
- The Pleistocene (Saber-Tooth Cats, Mastodons, etc.) lasted until about 11,000 years ago.
- The Anthropocene (the Epoch when Man changed EVERYTHING).
Until recently, the last ~11,000 years have been just called the Holocene. Now the Holocene has been divided up to add a more recent epoch: the Anthropocene: The Time When Man Started Changing Things. A singular characteristic: in the last century, mass-extinctions have accelerated so fast (Kolbert, 2014) that it's comparable to the extinction event that ended the age of dinosaurs. Instead of a killer asteroid this time, it’s… humankind.
There are a number of other Signs of the Times, but this may be the most seriously under-estimated one.