Next up, we have a speaker who really needs no introduction. For over four decades, he's been one of the most courageous voices in climate science, the scientist who first brought global warming into the world's attention when he testified before the US Congress in 1988. He's the former director of NASA's Goddard Institute for Space Studies and current director of the climate science awareness and solutions program in at Colombia University.
His groundbreaking research on climate sensitivity and radiative forcing has really shaped our fundamental understanding of the earth's climate system. We had the extraordinary opportunity to collaborate with him on his latest paper on the acceleration of global warming and that's work that directly speaks to why we're all here today. So please welcome to the stage Dr. James Hansen.
1.00
I'm glad to have the chance to speak with you. I'm quite impressed that Finland is very pragmatic and I hope that can provide some leadership to some other countries which are not being so pragmatic. So I'll go to my second chart.
when I testified to the United States Senate in 1988 that I had a high degree of confidence that the world had entered a period of long-term warming spurred by human-made gases, there was near universal condemnation by the scientific community, as described in an article in Science titled Hansen versus the world.
But my conclusion was not based on statistics of the global temperature curve. Other information included the paleoclimate response to Earth orbital variations. the cooling that occurred after Mount Aegong exploded in s and knowledge of greenhouse gas forcings and so on a wide range of information.
2.27
Today, global warming is accelerating by increasing greenhouse gases plus reduced particulate air pollution, especially from East Asia and ships at sea. We do not need to wait 10 years to conclude that we have reached 1.5 degrees global warming. Satellite data show that Earth is strongly out of energy balance. More energy coming in than going out. So Earth will be getting still warmer.
An important factor is that IPCC's the Intergovernmental Panel on Climate Change, best estimate of climate sensitivity is a substantial underestimate. I will show that tomorrow in several independent ways.
Climate sensitivity is probably between four and 5° C for doubled CO2 rather than 3 °. The upshot is that humanity has a larger price to pay than expected. That's a big problem. Technically it's solvable if humanity has its wits about the matter.
So I was glad to meet the young people who want to have a voice in their future and that's why I came to this meeting.
4.07
Scientific reticence is dangerous in a problem that has delayed response. Reticence described by Fineman embarrassed physicists, but it didn't harm anybody. What we witness now is scientific reticence on steroids. Perhaps because IPCC was granted the position of supreme authority.
But in science, supreme authority is not granted to anyone. Galileo proved that.
An example of expert herd mentality is the response to our global warming acceleration paper which Annie was co-author on. The next day, these experts unanimously condemned our paper in the media. Not one of them discussed the physics in our paper or explained what was wrong. Instead, there were ad homonym remarks. Hansen makes lots of mistakes. Hansen exaggerates. Hansen is not collegial. What could the media do? They dropped the paper. No more discussion of it.
Juel Charnie, Francis Bretherton would be shocked by this non-science nonsense. Why does this matter? The Secretary General, the United Nations, the body advised by the IPCC keeps saying we can keep global warming to 1.5C via net zero emissions by 2050.
6.30
What hogwash. You will not see this figure in an IPCC document. It exposes too much. Greenhouse forcing is still increasing almost half a watt per decade. IPCC once defined a scenario RCP 2.6 that would keep global warming near 2 degrees C. The real world is closer to RCP 8.5. Direct air capture of CO2 to close that gap would cost trillions of dollars per year. It's not going to happen. Global warming will exceed 2°.
Now, for some crucial physics, tipping points have become mighty popular, but be careful in talking about them. Many are just reversible amplifying feedbacks. If we take action to make Earth's energy balance negative, they reverse and amplify cooling.
The danger is a tipping point that can accelerate and pass a point of no return with consequences that cannot be reversed on any time scale that people care about.
A prime example is shutdown of North Atlantic deep water formation, which I will discuss tomorrow and we're going to hear from the world's expert on it in a few minutes Stefan Ramsttorm.
8.18
I will argue that we are on track for shutdown within a few decades and in turn this will accelerate melting of Antarctic ice shelves and large sea level rise. That figure is in a paper we submitted in 2015 and published in 2016. Our science analysis was based on our use of all sources: paleoclimate, climate models, and modern data.
One reviewer, an IPCC lead author, was determined that the paper never be published, while the other reviewer described the paper as a master work of scholarly synthesis, modeling, virtuosity, and insight with profound implications. So two added reviewers were needed who approved the paper.
But the story of how the editorial board forced us to change the title “two degrees is highly dangerous” to “could be dangerous” should stand your hair on end. And I'm going to tell that story tomorrow.
Understanding future climate requires a broad scientific approach including energy science. To halt global warming we must reduce carbon intensity to near zero by mid century. But in half a century we have reduced it only from point 8 to 7. Data show that Sweden and France got halfway there with nuclear power, but the world neglected the chance to develop more capable nuclear to complement renewables.
Why did IPCC stand by when Germany insisted that nuclear be disallowed as a clean development mechanism? What good are advisors who do not advise?
10.32
We know that fossil fuel emissions, we know where they're coming from. China is now the largest source. China, the US, and India produce half of global emissions. But global warming is well approximated by cumulative historical emissions. So the US is the greatest cause of global warming. On a per capita basis, the responsibility of the west is even greater.
But emerging economies and developing nations will have a bigger role in the future. So nations must cooperate. We all live on the same planet and face the same future.
The entire climate story, the actions needed to achieve a stable climate are subject to scientific inquiry. As scientists, we should not sherk from investigating issues and offering conclusions and opinions for consideration by the public. I hope we have time tomorrow for some discussion of some of the fundamental issues even though the conference may be a little more narrowly focused but we're running out of time. Thanks. [Applause] All From
