CCNF ceased operations in February 2016, and this website is no longer active. Thank you to all the contributors that made the Forum a success. We had a good run! -MAQ

“What you need to know about climate change in 24 easy steps” [For fact checking & commentary]

December 16, 2014 1:36 am0 comments

I recently discovered this video—”What you need to know about climate change in 24 easy steps”—by Dr. Joe Hanson, a popular #SciComm writer and the creator-host of ‘It’s Okay To Be Smart‘ on PBS. I circulated a number of his steps on CCNF’s internal platform and received the following responses from Drs. Will Howard and Scott Denning, which I have included in colored text below.  I’m starting with the step on ocean acidification (OA), because we haven’t had much dialogue on that topic and now have a few experts in that area.


Dr. Joe Hanson in "Climate Change in 24 easy steps" on PBS Digital Studios' "It's OK to be Smart" series.

Regarding step #8 from the video, on understanding ocean acidification:

The oceans are earth’s largest carbon sink. As more carbon dioxide enters the atmosphere, more of it dissolves into the ocean, which makes the water more acidic. This doesn’t mean that the oceans will be made of acid, but animals with calcium shells are super sensitive to pH. We are on course for the oceans to hit a pH of 7.8 in a hundred years, which could wipe out one third of species in the ocean.


Dr. Will HowardDr. Will Howard: The first part—the oceans being on track for pH 7.8—is correct. We really don’t know what this means for extinctions. I don’t know what the basis is for the “one third of species” statement. However, the ecological impact we do have some basis for understanding is the effect of ocean acidification on important biological processes like calcification. We already have evidence for reduced calcification in some corals and in planktonic foraminifera. So what is most directly and immediately at risk is not so much the *existence* of species but their roles in the ecosystems—such as the roles of corals and calcifying algae in building and maintaining habitats such as reefs.

Dr. Scott DenningDr. Scott Denning: I agree the “one third of ocean species” claim is poorly defined and probably wrong. Ocean acidification is more about depletion of carbonate that marine organisms use to build shells and other body parts than about pH.

Step #3: “Human activity has increased [atmospheric] carbon dioxide 40% since the industrial revolution.”

WH: This is correct. Atmospheric pCO2 has gone from its preindustrial ~ 280 ppmV level to ~ 400 ppmV now.

Step #6:  “Since 1870 – with fossil fuel use, cement production, and land use combined – humans have put about 2,000 gigatons of CO2 in the atmosphere—that’s two million million tons, and about 40 % has stayed there.”

WH: That’s about right to my understanding. See the Global Carbon Project for more detail:

Step #7:  “Studying gases trapped in ice cores has let us see what earth’s atmosphere was like in the past. At more than 400 ppm, today’s CO2 levels are the highest they’ve been for almost a million years. That’s before humans even existed – totally uncharted territory for us.

WH: Correct, and we are imposing a far greater rate of change of CO2 and other GHGs than we can estimate for the past based on the ice cores (see point below). So are pushing the capacity of natural systems (e.g. the buffering capacity of the ocean) to adjust to this perturbation.

SD: We have actual samples of air from ice cores going back over 800,000 years, and CO2 has never been this high in that time. Although we don’t have actual air from that time, proxy records show it’s been about 4 million years since CO2 was last 400 ppm. Long before Homo sapiens, and even well before our genus “Homo.”

Step #8: “…Right now the earth is warming ten times faster than at the end of an ice age.”

WH: Maybe faster.

SD: Recent reconstruction by Shakun et al (2012) shows the main warming after the last Ice Age was about 2 Celsius (globally) over 4000 years starting 16,000 years ago. That’s 0.005 Celsius per decade. Since 1980, global temperature has warmed 0.175 Celsius per decade, which is 35 times as fast as the climate warmed during the fastest part of the last deglaciation. #14 “In the 2000s, there were twice as many record highs as record lows. (RS/ US NAS), and each of past 3 decades has been warmer than any other decade since we started measuring in 1850.”

Step #9: “…Volcanoes admit only about 1 percent (around 0.2 gigatons/year) of the CO2 that we do.”

WH: Volcanoes emit less than 1 percent. We emit ~ 36 GT/yr, so it’s around 0.5 percent.

Step #15: “Since 1900, most of the world has increased a full degree (C) and most of that has happened since the 1970s.”

Step #17: “Ocean’s cover more than 70% of earth and absorb more than 90% of the heat added to the planet. Naturaly, that’s where we are seeing the most extreme changes.”

WH: Oceans have absobed about 90 % of the excess heat, or net radiative imbalance, the added GHGs have created. Not sure what he means by “the most extreme changes.”

SD: The extra heat in the ocean is “diluted” by their enormous heat capacity, so the changes in water temperature are mostly smaller than over land. Of course it’s that huge heat capacity that lets the oceans hold the heat, but the biggest temperature changes are over land.

Step #21: “The oceans are earth’s largest carbon sink. As more C02 enters the atmosphere, more of it dissolves into the ocean, which makes the water more acidic.”

WH: True.

Step #23: “We also know that levels of summer sea ice in the artic have decreased 40 % since 1978… That white sea ice usually reflects the sun’s energy back into the atmosphere, but the dark ocean is soaking up like a black shirt on a sunny day which feeds the cycle forward.

Step #24: “If CO2 emissions continue on their current trends, earth is on course to be 2.6 – 4.8 C (4.7 – 8.6 F) degrees warmer and the oceans could be up to a meter higher by the end of this century.

SD: This is from the RCP8.5 emission scenario, which involves very rapid increases in CO2 emissions as developing countries industrialize their economies. It’s sometimes called the “no policy” scenario. Many experts think sea levels would rise even more in this scenario.

Correction: In the quote for step #6, I originally misquoted Dr. Hanson as saying that “humans have put about 2,000 Gigatons (a Gigaton = a million millions) of CO2 in the atmosphere… and about 40% has stayed there”. This was an incorrect transcription on my part, and Dr. Denning spotted the error. Dr. Hanson actually said that “humans have put about 2,000 Gigatons of CO2 in the atmospherethat’s two million million tons—and about 40% has stayed there,” which is a correct statement according to Dr. Denning. I have since made the correction to reflect as much. Thank you @P_aulina for first spotting my error, and apologies to Dr. Hanson. -MQ

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