We may be pushing the planet towards some limits which will not be healthy at all for Homo sapiens or for our societies? There are at least nine processes or parts of the earth's systems that we need to respect. We now have climate change. What's our control variables?
1. Carbon dioxide. We shouldn’t go above 350 parts per million CO2 to stay within the safe Holocene type of environment. We are now at 387.2. We're in overshoot.
2. Nitrogen cycle. We actually now pull nitrogen out of the atmosphere, unreactive nitrogen and through industrial processes, turn it into reactive nitrogen, spreading it across landscapes. We needed to grow food. The food actually takes up a small percentage. The rest of it moves out as pollution, polluting ground water, the atmosphere, and coastal seas.
3. Biodiversity loss. There are other important losses too, ozone depletion, aerosol loading.
4. Acidifying the ocean.
5. Global freshwater use. We're using nearly half of the water now that flows to the ocean. There's not much left for the rest of the species on the planet. Where should we draw the line?
6. Boundaries are an important concept because once we define where the boundaries are, then they define a safe operating space where humanity can maneuver.
7. Equity issues.
8. Economic growth.
9. Biological species. We live on a planet, and we need to respect the boundaries of the planet itself intrinsically sets for us.
Summary, we have moved into the Anthropocene. Whether we should stay there is a decision we should talk about as a global community because, in the end, the risk associated with the Anthropocene will really push us past some limits and like earlier civilizations, there is no guarantee civilization lasts forever. The Romans aren't around nor the Mayans. We might not be unless we start thinking globally, as well as locally.
In this depressing interview, Guy McPherson makes a case that we've already pushed past some limits.
"A suite of amplifying feedback loops have engaged ..."
"the clathrate gun may have been triggered in 2007..." ("clathrate gun" refers to self-amplifying methane emissions)
(paraphrase) (Nature 2013) A 50 Gigaton burp of methane is highly likely - that's 3 times what we’ve released since the beginning of the industrial revolution, being released within weeks or months.
McPherson explains that people won't die directly from overheating so much as from starvation. "People will die because the plants and plankton can’t respond very quickly." "At 125 to 130 degrees proteins denature in plants." "We’ve already lost about half of ocean plankton from the 0.85C rise." Last I'd heard only 40% of ocean plankton had died, but I may be out of date.
The only thing he said which I question is the chart showing a parabolic curve for upcoming temperature rise. The data points shown don't justify fitting to a parabolic function. It's this questionable graph he uses to make the most scary predictions, such as, "More than 4 C rise above baseline by so 2030 or 10 C by 2040." While it makes sense that positive feedback will generate far more than linear rise, I don't see data yet to justify an exponential rise. Remember some climate scientists still think that the Arctic won't be completely ice free until mid century, so this is an extreme model.
Everything else he quoted, I'd read from other sources I trust. Of course I'm not ready to give up on the future yet, to just live in the here and now.
Here's a critique of the questionable graph I mentioned above, by a hydrogeologist, geoscience educator, and freelance science writer Scott K Johnson.
What is this prediction based on? Curves drawn on a chart. If you fit the right polynomial (a dangerous activity) to the Arctic temperature data that shows roughly 2C warming from 1980 to 2010, you can get it to skyrocket to 20C by 2050. (Well, actually you can’t quite, so a steeper line is simply drawn on.) No climate model. No physics. Just a line. This isn’t science. This is the kind of thing that lazy climate “skeptics” do (the smarter ones won’t).
So Johnson is saying that this is just an extrapolation of the rate of Arctic temperature rise from 1980 to 2010. We know that the Arctic rises significantly faster than the globe as a whole, so on the face of it McPherson is misleading the public to speak as if this were a global projection.