Explaining climate change science & rebutting global warming misinformation
Scientific skepticism is healthy. Scientists should always challenge themselves to improve their understanding. Yet this isn't what happens with climate change denial. Skeptics vigorously criticise any evidence that supports man-made global warming and yet embrace any argument, op-ed, blog or study that purports to refute global warming. This website gets skeptical about global warming skepticism. Do their arguments have any scientific basis? What does the peer reviewed scientific literature say?
Posted on 28 February 2015 by John Hartz
- A cause for pause? Scientists offer reasons for global warming 'hiatus'
- A February first: CO2 levels pass 400 PPM milestone
- AMS: Dem’s climate-funding probe sends ‘chilling message’
- Coral collapse millennia ago may preview global warming impact
- Even as the eastern U.S. freezes, there’s less cold air in winter than ever before
- Five decisions the IPCC made today about its future
- Glacial melting in Antarctica makes continent the 'ground zero of global climate change'
- Majority of Americans agree fighting climate change a 'moral obligation'
- NASA satellites start tracking down the sources of climate change
- Official data confirms Chinese coal use fell in 2014
- Peak fossil fuel won’t stop climate change – but it could help
- Switzerland first to submit climate plan for Paris U.N. deal
- We could keep a huge amount of carbon out of the atmosphere just by changing people’s behavior
- What happened to the lobbyists who tried to reshape the US view of climate change?
- World should not rush to judge Paris climate deal, says top US negotiator
A cause for pause? Scientists offer reasons for global warming 'hiatus'
It's been dubbed both a "pause" and a "faux pause," and it's ignited debate among climate scientists and their critics.
After a period of rapid global warming throughout most of the 20th century, the pace of global temperature rise has slowed greatly over the last 10 to 15 years.
This unexpected slowdown has raised questions about the accuracy of climate change forecasts, and sent scientists searching for an explanation.
A cause for pause? Scientists offer reasons for global warming 'hiatus' by Monte Morin, Los Angeles Times, Feb 26, 2015
Posted on 27 February 2015 by greenman3610
Above, my newest “This is Not Cool” video focuses on the backstory behind “Merchants of Doubt”, the new documentary inspired by Naomi Oreskes’ and Eric Conway’s book of the same name. The centerpiece of the book is the story of how techniques of science denial perfected in the tobacco industry have been adapted to the broader war on inconvenient science.
This week’s media firestorm centering on Dr. Willie Soon, a high profile prop at many a gathering of climate deniers, was kicked off by Justin Gillis’ piece in the New York Times on Sunday:
It’s not insignificant that Gillis put the affair in a larger context, something that happens rarely in media coverage of the climate issue.
Posted on 26 February 2015 by John Hartz
- Climate change is not just an environmental issue
- Climatology versus Pseudoscience book tests whose predictions have been right
- Effective communication, better science
- Effects of climate change on wheat will be dire
- European leaders push for energy union
- IPCC chair Rajendra Pachauri resigns
- On Keystone and climate, Bloomberg presses Obama to negotiate with Canada instead of Congress
- Lobbyist dubbed Dr Evil behind front groups attacking Obama power rules
- Researchers think they’ve found a “gateway belief” that leads to greater science acceptance
- Sardines swim into northern waters to keep cool
- Scientists witness carbon dioxide trapping heat in air in real-time field measurements
- Tar Sands pipeline vetoed, climate threat marches on
- The troubling psychology of how we decide who’s a scientific “expert”
- Uncertainty behind climate projections could be cut in half by 2030
- With climate change, US presidents matter
Climate change is not just an environmental issue
The general election means 2015 is a critical year for Britain. It is also a critical year for the world on climate change. Within months of Britain voting, the UN is holding a summit in Paris to agree a binding global agreement to tackle climate change.
But there is a real danger that this great chance to achieve action is going to slip by, without the world even noticing. That might suit some politicians at home but it will be a disaster for our country and the world.
Climate change is not just an environmental issue, Op-ed by Ed Miliband, The Guardian, Feb 21, 2015
Posted on 26 February 2015 by Guest Author
This is a guest post by Zeke Hausfather
There has been much discussion of temperature adjustment of late in both climate blogs and in the media, but not much background on what specific adjustments are being made, why they are being made, and what effects they have. Adjustments have a big effect on temperature trends in the U.S., and a modest effect on global land trends. The large contribution of adjustments to century-scale U.S. temperature trends lends itself to an unfortunate narrative that “government bureaucrats are cooking the books”.
Having worked with many of the scientists in question, I can say with certainty that there is no grand conspiracy to artificially warm the earth; rather, scientists are doing their best to interpret large datasets with numerous biases such as station moves, instrument changes, time of observation changes, urban heat island biases, and other so-called inhomogenities that have occurred over the last 150 years. Their methods may not be perfect, and are certainly not immune from critical analysis, but that critical analysis should start out from a position of assuming good faith and with an understanding of what exactly has been done.
Posted on 25 February 2015 by John Abraham
Yesterday, President Barack Obama became the first president who has taken a stand to stop climate change.
Actually, that isn’t quite true. President Obama took that stand from his first step into the White House. He has put into place a series of initiatives that actually give us a chance at stopping the most serious consequences of climate change. Much of his actions have gone with little public notice. That changed yesterday with his veto of the ill-proposed Keystone XL pipeline.
Vetoing this pipeline, which would increase the rate of extraction of the world’s dirtiest fuels (bitumen and the byproduct petroleum coke), was a no-brainer for anyone concerned about climate change. In fact, it is not possible to be in favor of the Keystone pipeline if you accept the science of climate change. The reason this story is so big isn’t just about carbon dioxide emissions (although that matters). It is more about the strong stand taken by the President against a well-funded campaign to force the pipeline through. It is also important because of the signal it sends to those intent on long term dirty-fuels extraction.
Let’s quickly summarize why the Keystone pipeline was a bad idea to begin with. First, by lowering the production costs, it will increase the rate of extraction of the dirtiest fuels in the world. Second, it will actually raise fuel prices in the United States where much of the tar sands is now sold at a discount. Third, the pipeline will lock in decades of production of dirty fuel even as the costs to deliver wind and solar energy are falling fast and becoming comparable with fossil fuels. Finally, the pipeline would have traversed the United States and would have presented a large spill risk. Why can’t the Canadian government just put the pipeline through their own country? The reason is, their own citizens object.
Back to President Obama. His actions on climate change are numerous and significant. As outlined in his Climate Action Plan, his administration has overseen large investments in renewable energy industries in the U.S. that are creating high-pay and high-skill jobs. He has enacted increases in fuel-efficiency standards which not only reduce emissions but also save money. He has worked on international agreements to reduce hydrofluorocarbons and methane emissions, two potent greenhouse gases.
Posted on 24 February 2015 by John Hartz
This bulletin also functions as a supplemenatry reading list to two recently posted SkS articles rebutting Booker's false claims and innuendos, i.e.,
Climate Change Denial at Its Worst? by Feb 14, 2015
Climate Denial Empire Strikes Back with Bogus Temperature Story by Peter Sinclair, Climate Crock of the Week, Feb 10, 2015
Climate Denial Food Chain: Conservative Media Run With Baseless Climate Science Conspiracy Theory, Research by Denise Robbins, Media Matters, Feb 10, 2015
Climate science denialists in tailspin over hottest years, The Planet Oz by Graham Readfearn, The Guardian, Feb 12, 2015
Evil Nazi-communist world-government climatologists have manipulated data to REDUCE global warming by Victor Venema, Variable Variability, Feb 10, 2015
Fiddling with global warming conspiracy theories while Rome burns by Dana Nuccitelli, Climate Consensus - the 97%, The Guardian, Feb 11, 2015
Fox News has no shame: Easily duped wingnuts spout phony science and climate-change lies by Brad Friedman, Brad's Blog, Feb 19, 2015
Fox News host: Climate scientists 'fabricated' temperature data by John Greenberg, PolitiFack.com, Feb 13, 2015
Fox News' Special Report Advances Debunked Claim That Climate Change Data Is "Cooked", Media Matters, Feb 10, 2015
Noise on the Telegraph by Rasmus Benestad, Real Climate, Feb 11, 2015
Scientists dismiss claims of "fiddling" global temperature data by Roz Pidcock, The Carbon Brief, Feb 10, 2015
Temperature data is not “the biggest scientific scandal ever” by John Timmer, Ars Technica, Feb 9, 2015
Why scientists adjust temperature records, and how you can too by Neville Nicholls, The Conversation US Pilot, Jan 27, 2015
Posted on 24 February 2015 by Kevin C
There has been a vigorous discussion of weather station calibration adjustments in the media over the past few weeks. While these adjustments don't have a big effect on the global temperature record, they are needed to obtain consistent local records from equipment which has changed over time. Despite this, the Telegraph has produced two highly misleading stories about the station adjustments, the second including the demonstrably false claim that they are responsible for the recent rapid warming of the Arctic.
In the following video I show why this claim is wrong. But more importantly, I demonstrate three tools to allow you to test claims like this for yourself.
The central error in the Telegraph story is the attribution of Arctic warming (and somehow sea ice loss) to weather station adjustments. This conclusion is based on a survey of two dozen weather stations. But you can of course demonstrate anything you want by cherry picking your data, in this case in the selection of stations. The solution to cherry picking is to look at all of the relevant data - in this case all of the station records in the Arctic and surrounding region. I downloaded both the raw and adjusted temperature records from NOAA, and took the difference to determine the adjustments which had been applied. Then I calculated the trend in the adjustment averaged over the stations in each grid cell on the globe, to determine whether the adjustments were increasing or decreasing the temperature trend. The results are shown for the last 50 and 100 years in the following two figures:
Posted on 23 February 2015 by dana1981
I’ve just had a book published entitled Climatology versus Pseudoscience: Exposing the Failed Predictions of Global Warming Skeptics.
The book covers a wide range of climate-related topics, starting with a history of some key discoveries in the field of climate science beginning nearly 200 years ago. Along the way it debunks some common climate myths, progressing forward in time to the 1970s, when scientists’ ability to model the global climate began to advance rapidly. It examines the accuracy of a variety of global warming projections, starting with J.S. Sawyer in 1972, through the recent IPCC reports, as well as some predictions by contrarians like Richard Lindzen.
Posted on 22 February 2015 by John Hartz
Missing Arctic warming does contribute to the hiatus, but it is only one piece in the puzzle by Kevin C generated the most chatter of the articles posted on SkS during the past week.
For years, politicians wanting to block legislation on climate have bolstered their arguments by pointing to the work of a handful of scientists who claim that greenhouse gases pose little risk to humanity.
One of the names they invoke most often is Wei-Hock Soon, known as Willie, a scientist at the Harvard-Smithsonian Center for Astrophysics who claims that variations in the sun’s energy can largely explain recent global warming. He has often appeared on conservative news programs, testified before Congress and in state capitals, and starred at conferences of people who deny the risks of global warming.
But newly released documents show the extent to which Dr. Soon’s work has been tied to funding he received from corporate interests.
Deeper Ties to Corporate Cash for Doubtful Climate Researcher by Justin Gillis & John Schwartz, New York Times, Feb 21, 2014
Toon of the Week
Posted on 21 February 2015 by John Hartz
- A look behind the headlines on China’s coal trends
- A melting Arctic and weird weather: the plot thickens
- California water becomes scarce and energy hungry
- Canadian mounties' secret memo casts doubt on climate change threat
- Catholics fast for Lent in support of Pope Francis’ call for Climate Action
- Despite frigid conditions in the East, U.S. seeing more record warmth this winter
- EU introduces new rules to make cooking greener
- Fox News has no shame: Easily duped wingnuts spout phony science and climate-change lies
- Global warming is going to hammer New York: New study reveals a future of heat waves, downpours, rising seas
- Making sense of climate science denial
- New hopes that tar sands could be banned from Europe
- Scientist finds remarkable way to connect people emotionally with climate change
- Solar energy’s new best friend is … the Christian Coalition
- Unprecedented California sea lion strandings linked to warmer Pacific
- World's biggest PR firm calls it quits with American oil lobby – reports
A look behind the headlines on China’s coal trends
Armond Cohen at Clean Air Task Force has provided helpful context in the face of recent headlines and a Greenpeace analysis focused on what appears to be the first drop in Chinese coal use in a century.
A Look Behind the Headlines on China’s Coal Trends by Andrew Revkin, Dot Earth, New York Times, Feb 18, 2015
Posted on 20 February 2015 by Guest Author
Everyone loves to talk about the weather, and this winter Mother Nature has served up a feast to chew on. Few parts of the US have been spared her wrath.
Severe drought and abnormally warm conditions continue in the west, with the first-ever rain-free January in San Francisco; bitter cold hangs tough over the upper Midwest and Northeast; and New England is being buried by a seemingly endless string of snowy nor’easters.
Yes, droughts, cold and snowstorms have happened before, but the persistence of this pattern over North America is starting to raise eyebrows. Is climate change at work here?
Wavier jet stream
One thing we do know is that the polar jet stream – a fast river of wind up where jets fly that circumnavigates the northern hemisphere – has been doing some odd things in recent years.
Rather than circling in a relatively straight path, the jet stream has meandered more in north-south waves. In the west, it’s been bulging northward, arguably since December 2013 – a pattern dubbed the “Ridiculously Resilient Ridge” by meteorologists. In the east, we’ve seen its southern-dipping counterpart, which I call the “Terribly Tenacious Trough.” (See picture, below.)
These long-lived shifts from the polar jet stream’s typical pattern have been responsible for some wicked weather this winter, with cold Arctic winds blasting everywhere from the Windy City to the Big Apple for weeks at a time.
We know that climate change is increasing the odds of extreme weather such as heatwaves, droughts and unusually heavy precipitation events, but is it making these sticky jet-stream patterns more likely, too? Maybe.
Posted on 18 February 2015 by John Hartz
- ‘Anti-petroleum’ movement a growing security threat to Canada, RCMP say
- Australian Academy of Science brings climate change closer to home
- Australian scientists make fresh attempt at explaining climate change
- BP's two-word fix for global climate change
- Climate change could decimate the American ski industry
- Global ocean acidity revealed in new maps
- How significant is the UK party leaders' joint climate pledge?
- Jury in on climate change, so stop using arguments of convenience and listen to experts
- Naomi Klein on how to build a more kick-ass climate movement
- NASA climate study warns of unprecedented North American drought
- Risk of American 'megadroughts' for decades, NASA warns
- Staying afloat amid climate change
- These countries are making polluters pay
- Warming planet threatens more and possibly deadlier pathogens
- What the massive snowfall in Boston tells us about global warming
Anti-petroleum’ movement a growing security threat to Canada, RCMP say
The RCMP (Royal Canadian Mounted Police) has labelled the “anti-petroleum” movement as a growing and violent threat to Canada’s security, raising fears among environmentalists that they face increased surveillance, and possibly worse, under the Harper government’s new terrorism legislation.
In highly charged language that reflects the government’s hostility toward environmental activists, an RCMP intelligence assessment warns that foreign-funded groups are bent on blocking oil sands expansion and pipeline construction, and that the extremists in the movement are willing to resort to violence.
“There is a growing, highly organized and well-financed anti-Canada petroleum movement that consists of peaceful activists, militants and violent extremists who are opposed to society’s reliance on fossil fuels,” concludes the report which is stamped “protected/Canadian eyes only” and is dated Jan. 24, 2014. The report was obtained by Greenpeace.
‘Anti-petroleum’ movement a growing security threat to Canada, RCMP say by Shawn McCarthy, The Globe & Mail, Feb 17, 2015
Posted on 18 February 2015 by Glenn Tamblyn
An old saying in marketing and communications says: ‘Repeat it, and repeat it, and repeat it again. When you are tired of repeating it, people might just start to take notice’. Sometimes this can seem oh too true. Particularly where warnings about unexpected dangers are concerned.
In 1951 U.S. President Harry Truman established the Science Advisory Committee as part of the U.S. Office of Defense Mobilization. After the launch of Sputnik in 1957 President Eisenhower renamed it the President’s Science Advisory Committee and moved it into the White House.
The committee wrote many reports for U.S. presidents, often on defense issues. But they also produced a large report – ‘Restoring The Quality of Our Environment’ – tackling a wide range of environmental and pollution problems of the time.
Included within this report was a 23 page appendix, ‘Appendix Y4 – Atmospheric Carbon Dioxide’.
This was the first official report to any government anywhere in the world on the possible challenge rising Carbon Dioxide (CO2) levels in the atmosphere might pose. The report was presented to President Lyndon Johnson in 1965;
Half a century ago!
President Johnson made a speech to Congress about the report, including a reference to rising CO2 levels.
Posted on 17 February 2015 by Kevin C
A new paper from scientists at the Danish Meteorological institute investigates the geographical distribution of warming over the period of the recent slowdown. Interestingly they fail to find any significant contribution from the omission of the rapidly warming Arctic from some temperature datasets. This is surprising, given that the DMI's own data, as well as the AVHRR satellite data, the major weather model reanalyses and land based weather stations all show rapid Arctic warming at a rate which should affect global trends.
We have reproduced their work and established the reasons for their result. Gleisner and colleagues fail to find the impact of Arctic warming for three reasons: where they are looking for it, how they are looking for it, and when they are looking for it. We will consider each of these questions in turn.
First: A sanity check
First let's do a very simple sanity check to see if missing out the Arctic should have a noticeable effect on Arctic temperature trends.
HadCRUT4 had on average 64% coverage for the region north of 60°N for our original study period of 1997-2012. This region corresponds to about 6.7% of the planet's surface. Therefore the missing region corresponds to about 2.5% of the planet. Eighty percent of the missing region is north of 70°N where coverage is very incomplete.
The rate of Arctic warming in the MERRA for region north of 70°N, where most of the missing coverage occurs, is 1.3°C/decade. The ERA-interim reanalysis shows a higher rate of 1.7°C/decade. (Check it yourself)
The trend for the rest of the world is much smaller. Therefore, the missing region in the Arctic alone should increase the global trend by roughly 0.03 to 0.04°C/decade. The trend in HadCRUT4 over that period is about 0.05°C/decade. So inclusion of the Arctic alone might be expected to increase the global trend by 60-80%, as illustrated in Figure 1. Gleisner et al provide no explanation for the apparent contradiction between their results and the weather models.
Posted on 16 February 2015 by dana1981
California is in the midst of its worst drought in over 1,200 years, exacerbated by record hot temperatures. A new study led by Benjamin Cook at Nasa GISS examines how drought intensity in North America will change in a hotter world, and finds that things will only get worse.
Global warming intensifies drought in several ways. In increases evaporation from soil and reservoirs. In increases water demand. It makes precipitation fall more as rain and less as snow, which is problematic for regions like California that rely on snowpack melt to refill reservoirs throughout the year. It also makes the snowpack melt earlier in the year. The record heat has intensified the current California drought by about 36%, and the planet will only continue to get hotter.
Posted on 15 February 2015 by John Hartz
Dana's Fiddling with global warming conspiracy theories while Rome burns garnered the most comments of the articles posted on SkS during the past week. Tied for second place were Why the Miocene Matters (and doesn’t) Today by howardlee and A 23-year experiment finds surprising global warming impacts already underway by Dana.
Blog Posts We Like
Here’s one of the better produced videos you’ll see on climate change, not so much because of the flashy b-roll but because the scientist cuts right to the chase. It’s part of a series called Climate Change Elevator Pitch and comes courtesy of Climate Denial Crock of the Week. The host of the series is John Cook. He’s the Climate Communication Fellow for the Global Change Institute at the University of Queensland in Australia. He’s one of many people behind Skeptical Science, a fantastic resource to learn about climate change. You can spend hours there and barely touch the surface.
Climate Change Made Easy to Understand by Dan Bewley, Science is OK, Feb 2015
Toon of the Week
Hat tip to I Heart Climate Scientists.
Posted on 15 February 2015 by John Hartz
This article is a lightly edited version of a news release posted by the National Academy of Sciences (NAS) on Feb 10, 2015.
Proposed Intervention Techniques Not Ready for Wide-Scale Deployment
There is no substitute for dramatic reductions in greenhouse gas emissions to mitigate the negative consequences of climate change, a National Research Council committee concluded in a two-volume evaluation of proposed climate-intervention techniques. The two reports are:
- Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration
- Climate Intervention: Reflecting Sunlight to Cool Earth
Strategies to remove carbon dioxide from the atmosphere are limited by cost and technological immaturity, but they could contribute to a broader portfolio of climate change responses with further research and development. Albedo-modification technologies, which aim to increase the ability of Earth or clouds to reflect incoming sunlight, pose considerable risks and should not be deployed at this time.
Carbon dioxide removal and albedo-modification techniques have been grouped up until now under the common term “geoengineering,” but they vary widely with respect to environmental risks, socio-economic impacts, cost, and research needs. Carbon dioxide removal addresses the root cause of climate change — high concentrations of the greenhouse gas in the atmosphere — and generally have well-understood benefits and risks, but current technologies would take decades to achieve moderate results and be cost-prohibitive at scales large enough to have a sizeable impact. By contrast, albedo-modification techniques would only temporarily mask the warming effect caused by high CO2 concentrations, and present serious known and possible unknown environmental, social, and political risks, including the possibility of being deployed unilaterally.
Posted on 14 February 2015 by John Hartz
- Climate hacking is barking mad
- Climate science denialists in tailspin over hottest years
- Exclusive: Bjorn Lomborg think tank funder revealed as billionaire Republican 'Vulture Capitalist' Paul Singer
- Fiddling with global warming conspiracy theories while Rome burns
- Geoengineering might work in a rational world … sadly we don’t live in one
- Investments in African schools, health and other infrastructure exposed to climate risks
- Is climate change fuelling war?
- Nations agree draft text for deal to fight climate change
- Scientists urge global 'wake-up call' to deal with climate change
- Senators debate whether climate change is real at EPA Carbon Rule Hearing
- Significant errors in study suggesting global warming is good for the world
- Surprisingly, a voluntary climate treaty could actually work
- Using anti-Apartheid divestment strategies to battle fossil fuels
- What to call a doubter of climate change?
- White House: Climate change threatens more Americans than terrorism
Climate hacking is barking mad
Some years ago, in the question-and-answer session after a lecture at the American Geophysical Union, I described certain geoengineering proposals as “barking mad.” The remark went rather viral in the geoengineering community. The climate-hacking proposals I was referring to were schemes that attempt to cancel out some of the effects of human-caused global warming by squirting various substances into the atmosphere that would reflect more sunlight back to space. Schemes that were lovingly called “solar radiation management” by geoengineering boosters. Earlier I had referred to the perilous state such schemes would put our Earth into as being analogous to the fate of poor Damocles, cowering under a sword precariously suspended by a single thread.
This week, the National Research Council (NRC) is releasing a report on climate engineering that deals with exactly those proposals I found most terrifying. The report even recommends the creation of a research program addressing these proposals. I am a co-author of this report. Does this mean I’ve had a change of heart?
Climate hacking is barking mad by Raymond T. Pierrehumbert, Slate, Feb 10, 2015
Posted on 13 February 2015 by Guest Author
This is a re-post from Climate Lab Book
In a recent post on Climate Audit, Nic Lewis criticised Marotzke & Forster (2015, Nature) for applying circular logic to their arguments about forcing, feedbacks & global temperature trends. This is a guest post by Jochem Marotzke & Piers Forster replying to those criticisms.
It has been alleged that in Marotzke & Forster (2015) we applied circular logic. This allegation is incorrect. The important point is to recognise that, physically, radiative forcing is the root cause of changes in the climate system, and our approach takes that into account. Because radiative forcing over the historical period cannot be directly diagnosed from the model simulations, it had to be reconstructed from the available top-of-atmosphere radiative imbalance in Forster et al. (2013) by applying a correction term that involves the change in surface temperature. This correction removed, rather than introduced, from the top-of-atmosphere imbalance the very contribution that would cause circularity. We stand by the main conclusions of our paper: Differences between simulations and observations are dominated by internal variability for 15-year trends and by spread in radiative forcing for 62-year trends.
Posted on 12 February 2015 by howardlee
Past climate changes are analogs, albeit imperfect ones, for our modern climate change. Despite the differences between such episodes and today, they tell us a great deal about how the Earth-atmosphere-ocean-ice-vegetation-climate system responds to perturbations of the carbon cycle. Global warming in the Miocene at 16.9 million years ago is a mild example.
A time a bit like our own…
As we cross the 400ppm line in modern atmospheric CO2, we are entering climate territory not encountered for millions of years. We have to go back long before our ancestors evolved from apes – to the Miocene – to find CO2 at 21st Century levels.
…but not what we’re used to
For the duration of our genus (Homo) up to the industrial era, CO2 levels oscillated between around 180 and 280 ppm through the glacial-interglacial cycles of the ice ages. Before then in the Pliocene, as our Australopithecus ancestors like “Lucy” proliferated in Africa, CO2 was around 360-400ppm and global temperatures were on average about 3°C degrees warmer (but the Arctic was 7-8°C warmer) than today. Going further back into the Miocene, tropical sea surface temperatures were as much as 12°C warmer at 12 million years ago, with CO2 levels similar to today, estimated at around 400ppm. Ice was minimal in high northern latitudes and ice was restricted to inland portions of East Antarctica, while the rest of the continent supported temperate forests.
The Earth was on a multi-million-year cooling trend through the Miocene and Pliocene, which was slow enough to allow the feedbacks in Earth’s climate system to remain in equilibrium. But at 16.9 million years ago the Earth hit a bump in that cooling trend, an abrupt episode of global warming that was in some ways comparable to our own. This major perturbation of the Earth’s carbon cycle generated a 3-million-year-long greenhouse era known as the “Mid Miocene Climate Optimum” – mercifully shortened to MMCO.