This is an updated version earlier post, slightly shorter, where I have deleted some material in favour of new material, especially towards the end, and sharpening some points along the way.
Greta Thunberg, the girl who can’t quit, said:
- The emissions are increasing and that is the only thing that matters.
This is what was shown for July 01, 2019 at Mauna Loa:
[Update: For current data see NOAA’s Trends in Atmospheric Carbon Dioxide]
For longer time perspective, this one from 2017 shows what has happened since 1700:
This one shows the ice core record, going back 800,000 years:
What we’ve got now is outside human experience. It’s also a worry that during the last interglacial, the Eemian, sea levels were 6-9 metres higher than now with only 300 ppm.
As any primer on climate change will tell, the sun’s radiation comes in via a strong short wave, which punches through the atmosphere, but heat is emitted, mostly overnight, via a weaker long wave, which is more likely to be captured by CO2 molecules. They re-radiate the heat 360 degrees, so some of it is radiated back to the earth. Over 90 per cent of the heat ends up in the ocean:
James Hansen tells us in Climate Change in a Nutshell that the earth’s energy imbalance was measured as 0.75 ± 0.25 W/m2 from 2006-2016. That is less than a Christmas light bulb per square metre over the entire planet’s surface. However, Hansen does the maths, and it is equivalent to 400,000 Hiroshima atomic bombs per day, 365 days per year.
The second graph to watch is how energy is accumulating in the ocean. I don’t know of a constantly updated source, but this one shows what has happened in the upper 700 metres of the ocean in the last few decades, against a baseline of the average of 1955-2006:
A few of the bars of the mid-1980’s have been cut off a little, but the message is clear. Here’s one from Dana Nuccitelli from a few years ago:
As heat is distributed and the Earth system reaches equilibrium, some of the heat from the ocean will travel to the depths, but some will emerge to warm the atmosphere. So the third graph to watch is global surface temperature. NASA has an annually updated version. Here’s a screenshot:
I prefer this one from Hansen et al Global Temperature in 2018 and Beyond:
As the surface temperature warms, other effects manifest themselves, such as from the CSIRO/BOM State of the Climate 2018 report, an increase in extreme heat events:
changes in rainfall:
changes in ocean acidity:
and changes in sea level rise:
Given that the effects play out over centuries, indeed millennia, we need to go back to the paleoclimate record and look at analogues to get some idea of the longer term implications of current emission levels. It is common now to say, as this NASA site does, that today’s levels of CO2 are similar to the Pliocene, when the global surface temperature was roughly 3 to 4 degrees Celsius warmer than today and the sea 5 to 40 metres higher.
The point is that we are entering the zone where both Greenland and Antarctica are in play. Attenborough told us in his documentary that Greenland was now losing ice 5 times faster than 20 years ago, Antarctica three times. Stabilisation of ice sheets in the past has taken 1-4 millennia, according to Hansen. We have a couple of decades of data. It is salutary to realise that in the 2007 IPPC report they advised us that there was no worry about ice sheets because as the weather warms precipitation of snow would increase. Antarctica was expected to grow in the near term.
If you do the maths, two decades compared to 2 million years is the equivalent of five minutes in a year. We need to look more to paleoscience data, but there we have to remember that the disposition of the continents was different, as were the major ocean currents (the Panama Isthmus closed just over 3 million years ago.) In all probability the shape of the ocean basins was different. Finally we are now forcing the climate around 1000 times harder than it was changing naturally in the mid-Miocene.
The bottom line is that scientist don’t know how rapidly matters will proceed in the next century or three, but on sea level rise they are saying a 5 per cent chance of up to 2.5 metres by 2100, whereas the fifth IPCC from 2014, used by Attenborough, maxed out at 98cm.
Given that 3 degrees when added to current warming makes 4 degrees, which is held to be the point where civilisation as we know it is threatened, the implications are ugly, but we are some way from fully understanding them.
It may not end there. Stories such as Antarctic Sea Ice Declining ‘Precipitously’ Since 2014, Study Finds and Antarctica’s Ice Is Melting 5 Times Faster Than in the 90s are not what we want to hear. The last thing we need for a safe climate is ice sheets in play. Yet that is what we appear to have (from the NASA site). Greenland:
The Greenland ice sheet is worth 6-7 m in sea level rise, West Antarctica 5-7 m, and East Antarctica 59 m. With land glaciers and ice caps elsewhere at 0.5 m and thermal expansion the total is in the region of 75-80 metres.
A fundamental problem is our habit of burning fossil fuels. Here’s the fourth graph from Makiko Sato and James Hansen (see Nutshell p. 49):
Kenneth Rogoff tells us that while the average age of coal-fired power plants is 42 years in advanced economies, in Asia the average is only 11 years, and a new one is being built every week.
Moreover, gas, which hasn’t been mentioned above, is much touted as a climate-friendly transition fuel, which is essentially a scam. For starters greenhouse accounting typically counts methane as around 23 times more potent than CO2. In fact that is after 100 years. In the first year methane is around 100 more times as potent. The reference I’ve always used is Dessus et al 2008, where we find this graph:
An argument could be mounted that if our concern is the next 60 to 80 years a much higher ratio should be used.
Declarations of ‘climate emergency’ notwithstanding, there appears to be an attitude that we can do climate mitigation without disruption.
For a safe climate we need need to dial down greenhouse gases urgently, which will be disruptive and involve stranded assets.
This graph shows the ‘Scope 3’ emissions from our existing and projected fossil fuel exports, emissions that are counted in the countries where the fuels are burnt:
Future climate policy will need to take account of the fact that such emissions must largely cease if the planet is to have a decent future. Leaving aside ethical concerns, the economic risk of stranded assets is immense.
Stephen Rahmstorf’s recent article makes the point that delay in emissions reduction has a cost. Using a scenario where zero net emissions are to be achieved in 2045 from a peak in 2020. If we delay the start of emissions reduction to 2030 the target completion date needs to be brought forward to 2035:
Many scientists are stressing that emissions must peak by 2020 if the whole exercise is not to spin out of control.
See also Gavin Schmidt’s response to the IPCC Special Report on 1.5ºC, where he says, inter alia:
- near-term reductions in carbon emissions by ~70% are required to even stabilize CO2, and to stabilize temperature, even further (net) reductions are required. And worse still to stabilize sea level, eventual temperature drops would be required.
- The best time to start [reducing emissions] was 25 years ago. The second best time is today.
When the situation looks hopeless we must take the first step.
NOAA has a graph on methane trends:
Its Mauna Loa CO2 graph also shows the monthly seasonal variations.
They also have an Annual Greenhouse Gas Index (AGGI). This graph shows the annual GHG forcing:
Forcing if 2018 was 1.43 times 1990 levels. The CO2e in 2018 was calculated as 496. I would question whether methane is adequately represented.
Update 2 (29/9/19):
Tamino at Open Mind has a post on methane acceleration. having been steady from 1999 to 2007 it started rising. Then in 2014 it began to rise even faster. The following is a huge worry:
Nisbet et al. identify the increased rate of rise in those four years, and consider the implication for the Paris climate agreement. The stated goal is to keep global temperature rise “well below 2°C.” So far, all our plans, our computer models, our strategies that have a decent chance of accomplishing that goal have relied on no increase in CH4, some even rely on decreasing CH4 in the air. The fact that it’s going the wrong way, at increasing speed, is a genuine threat to our chances of success. (Emphasis added)
Update 3 (8/11/2020):