Before the Industrial Revolution in the 1800s, the concentration of carbon dioxide (CO2) in the atmosphere was about 280 parts per million (ppm). This means that for every million molecules in the atmosphere, about 280 of them were CO2.
However, climate.nasa.gov shows that we’ve burned so much coal and oil that atmospheric CO2 is now approaching 400 ppm. It hasn’t been this high for millions of years. The last time Earth’s atmosphere had this much CO2, our species (and many others) hadn’t yet evolved.
Scientists performed experiments in the 1800s which showed that CO2 absorbs heat better than it absorbs visible light, and concluded that increasing CO2 would warm the planet. More recently, scientists have studied the ancient climate by analyzing rocks, fossils, and gas bubbles trapped in ancient ice. They repeatedly got the same answer: increasing CO2 has amplified the ice age cycle, caused temperatures to spike during the end-Permian extinction and the Paleocene-Eocene Thermal Maximum, and even thawed Snowball Earth.
If the Sun got brighter, that would also warm the planet. However, satellites haven’t seen a significant change in the Sun’s brightness since 1950. In fact, scientific studies accounting for many natural factors tend to suggest that the Earth would have cooled slightly since 1950 if we hadn’t burned so much coal and oil.
What have we observed?
- The Earth’s surface is warming. Satellites confirm that the lower atmosphere is also warming, and thousands of Argo floats confirm that the deep ocean is also warming.
- Glaciers all over the world are melting and sliding into the ocean. The GRACE satellites have shown that Greenland and West Antarctica are losing ice at an accelerating rate.
- Arctic sea ice is melting so quickly that the Arctic ocean could be essentially ice-free in September by 2030. This would briefly expose most of the Arctic ocean to the atmosphere for the first time in
hundreds of thousandsthousands of years. (See this comment.)
Conclusion: The world is warming, and our skyrocketing CO2 emissions have very likely caused most of the global warming since 1950. That’s why 13 national science academies signed a joint statement in 2009 telling world leaders that “the need for urgent action to address climate change is now indisputable.” Sadly, we’re still pumping out CO2 at least 10 times faster than during the previous record high, which was set 250 million years ago… right before the end-Permian extinction.
What should we expect?
- Global warming makes heat waves and droughts more severe, which combine to increase the risk of wildfires.
- Precipitation will probably fall in more intense bursts, and wet regions will probably get wetter while dry regions get drier.
- Hurricanes might not be more frequent, but they will tend to be stronger because warmer oceans provide more energy for a hurricane’s heat engine.
- By 2100, the oceans will rise by about a meter (or more). This will flood some coastal cities and threaten more by adding onto the storm surges of stronger storms.
- Warmer oceans evaporate more water vapor into the atmosphere. Global warming is making winters shorter, but the added water vapor allows for more snow. Disappearing Arctic sea ice also weakens the Polar Vortex, letting cold Arctic air spill southwards. Update: See debate.
- Global warming is happening faster than many species can adapt by migrating or evolving. Unfortunately, the species that will thrive are mainly pests like insects and jellyfish.
- Some species we like to eat are vulnerable, which is disturbing because in the future there will be more humans to feed. For instance, rice grows 10% less with every 1°C of night-time warming.
- Our CO2 emissions are also acidifying the oceans, which threatens species like corals that are the foundation of many oceanic ecosystems.
What should we do?
Science can’t answer questions about what we should do, so here I speak as a human being rather than as a scientist.
I think we should reduce CO2 emissions as quickly as possible. For example, we could treat the CO2 waste from coal power plants like waste from nuclear plants. Currently, government regulations force nuclear plants to pay for waste disposal, but coal plants get to treat our atmosphere as a free sewer. Many economists support charging coal plants for their CO2 waste, and returning that money directly to us, the people. This will create jobs by jumpstarting a new industrial revolution based on clean energy, and improve the food and water security for future generations.
In the freely-available video series “Earth: The Operators’ Manual,” Richard Alley explains that switching to clean energy will cost about as much as building our sewer system. I doubt that many people would give up indoor plumbing just to save that money, so I’m baffled that so many people seem willing to risk the water and food security of future generations just to save that money. Personally, I think we should try to buy some time for future generations to clean up our mess.
Here’s an index of comments:
TinyCO2 helpfully corrects me regarding the age of permanent Arctic sea ice, and asks questions about the warming, etc.
Mike helpfully corrects me by linking a paper showing an ice free Arctic ocean in the early Holocene, and asks about GRACE and ICESat, aerosol and cloud uncertainties, attributing warming to climate cycles or humans, climate sensitivity, etc.
Pete Ridley supports Beck’s CO2 “record” and asks if I know something that Professor Wolff needs to be made aware of.
I correct “15 million years” after reading more recent research.
LOVO asks me to address some questions.
Sidd asks about Greenland’s missing 2013 melt season.