So we have a new climate agreement out of Paris today.
Ah. Only some parts are legally-binding (the emissions commitments are not), and those parts which are binding are technically extensions to an existing treaty and, as such, do not require Senate approval. Tricky. [WeatherUnderground]
However on the day after signing India reaffirmed that it intended to double its coal output (India is currently the 4th largest emitter. [Guardian]
What is adequate?
We really have no idea.
Back in the 1990s the best science suggested that a temperature rise of 2°C above pre-industrial temperatures would probably not lead to ecological catastrophe. And this has been the stated goal since then.
This year the average global surface temperature is expected to breach the 1°C mark and we are already seeming effects that 25 years ago were predicted for 2°C. In other words it is no longer possible to avoid catastrophic climate change. We are already too late. [Kevin Anderson]
For instance parts of the antarctic ice sheet have already passed a tipping point and entered a period of irreversible melting. The irreversible loss of the Amundsen ice sheet alone will raise sea-level by 1 meter in the next two centuries. [Guardian] The arctic ice cap is melting faster than expected, destroying ecosystems and the lives of humans dependent on those ecosystems. The incidence of “extreme” weather events is higher than expected.
To some extent this has been recognized at COP21 and the text now includes the aspiration to hold the level of warming to 1.5°C. However this has not resulted in anyone making a further commitment to reduce their emissions.
The commitments on the table are estimated to produce an increase somewhere between 2.7°C and 4°C, depending on whose climate models one looks at.
Some basic science
The earth has a large thermal mass. This means that it heats up slowly. Even if we were to stop producing any CO₂ (from non-ecosystem sources) the earth’s temperature would continue to increase for many decades.
We have a carbon budget. There is a limit to how much we can pump into the air before, eventually, the world will heat up by 2°C. The problem is that we can easily overshot that limit long before the temperature reaches 2°C.
Unfortunately no one knows what the carbon budget should be. We do know that about half of all carbon emitted gets quickly reabsorbed by plants, but the rest hangs around for centuries. Estimates suggest we can emit a range somewhere between another 100-400 gigatons of carbon. That’s a fairly wide uncertainty. [Yale] We are currently emitting approximately 35gigatons of CO₂ a year, and each year we emit more than we did the year before (though that increase is slowing). [Wikipedia, 2013 data] So at this rate we have anywhere from another 6 to 22 years before we would have locked in 2°C of warming. Unfortunately this dataset only includes CO₂ emissions. It does not include methane (which has a greater effect but is released in much smaller quantities), or water vapor, or other gasses. So worst case is we have about 5 years more of business as usual before for we guarantee 2°C warming eventually.
2°C is a global average
Some parts of the world are warming much more quickly than others. The oceans warm more slowly than the land. But there is a about twice as much ocean than there is land, and if the ocean takes longer to get to 2°C then the land will get there faster, and by the time the global temperature has averaged a 2°C increase the land temperature will be much higher.
The arctic heats up faster than the tropics, but the tropics have traditionally had a much narrower range of temperatures so in spite of that fact they will see exceptional conditions become normal much more rapidly. In both cases the ecosystems will not be able to adapt. In the arctic because there are large swings in temperature, polar ice caps disappear. In the tropics because the temperature is simply beyond what plants and animals can handle.
What about carbon capture?
Essentially all of the IPCC models which project that we will limit warming to 2°C require that we will have negative carbon emissions after about 2050. [Kevin Anderson] Not zero emissions, but negative. And this presupposes a technology we do not currently have.
We might develop it.
But as far as I know the funding for research into this area has been drastically cut in recent years. [Guardian]
In other words the paths the IPCC sees that might restrict warming to 2°C all depend on technology which does not exist and isn’t being developed. This is disturbing.
There are many areas of potential positive feedback which are not addressed by the IPCC, because we do not yet know enough to quantify them. And they are ignored in our climate models.
Melting permafrost will release a lot of methane into the atmosphere, a more potent heat-trapping gas than CO₂. This in term will lead to higher surface temperatures which will lead to more methane being released. We can see this happening but can’t quantify it. [Katia Moskvitch]
Warming ocean floors will release methane from methane hydrates with a similar feedback effect. [SWERUS-C3]
Warming tropics lead to droughts over the Amazon which leads to the death of rainforest trees which releases more CO₂ which leads to more warming and even fewer trees.
Ice and snow reflect more light and heat than oceans or land. As glaciers and ice caps melt the earth will absorb more heat meaning that more ice and snow will be lost.
This means that our current best guess are probably too conservative.
Sea level rise
With the ice caps and glaciers melting, and the ocean water warming and expanding, sea level is rising.
So far the global average is about half a foot higher now than it was 100 years ago. However the oceans aren’t rising at the same rate and on the east coast of the US the rise has been closer to a foot.
A paper posted on the next by [Hansen — Discussion] suggests that the sea level may rise 10ft in the next 50 years and 15ft by 2100. This may be a worst case scenario, but past experience with climate predictions suggests that worst case scenarios have happened more frequently than best case ones. And we are very ignorant here.
Some context: Hurricane Sandy had a storm surge of about 13ft in New York. Hugo had a maximum surge of 20ft near Charleston. Katrina’s surge was about 27ft.
So by the end of the century New York might be constantly under more water than it was at the worst of Hurricane Sandy.
This would wipe out many coastal cities. It would destroy much farmland. Many island nations would no longer exist.
How fast can a marsh adapt? If the sea level rises by 15ft and the shoreline moves inward by many miles then marshes, which are very productive ecosystems will be wiped out.
But I thought climate changed stopped after 1998
This is a lie.
I have had the above statement questioned. So, a brief recap. I pulled down this dataset. I applied a linear regression least squares fit to the following year ranges of the global mean temperature:
|1880-2014||T=.0068*(year-1998) + 14.36°C|
|1960-1984||T=.0118*(year-1998) + 14.35°C|
|1990-1998||T=.0230*(year-1998) + 14.49°C|
|1998-2014||T=.0108*(year-1998) + 14.52°C|
The important thing to note here is the change/year which was .0068°C/year over the historical record; it was .0230°C/year in the 90s, and .0108°C/year in the period of the hiatus. So not only has the global temperature increased since 1998, but it has increased faster than the historical rate and about the same rate as during the 70s. It did slow down dramatically from the 90s, but that can be explained by the Pacific Decadal Oscillation [Nature].
However surface temperature is not a good indicator of heat transferred to the earth. And since 1998 more heat has gone into the deep ocean than happened before. With this year’s El Niño less heat is going into the ocean deeps and the surface temperature is again increasing quickly.
Remember in the last decade we have seen 8 of the hottest years on record, and the top 13 hottest years have all been since 1997. There is about 1 chance in 3.7 million of this happening if the climate were not warming. [Climate Central] And unless something amazing happens in the next 3 weeks, 2015 will be even hotter.
But isn’t extra CO₂ good for plants? Won’t warmer weather make ecosystems more productive?
There is some evidence that more CO₂ will make plants happier, but the effect is slight.
Basically ecosystems have adapted to current conditions. Changing those conditions will, in almost all cases be a change for the worse.
European grain productivity has already been reduced. [Frances Moore] The current drought exacerbated (and possibly caused) by climate change has reduced California’s agricultural productivity. Global grain productivity is expected to fall at about 1.5% per decade [David Lobell] Grains produce less protein in hot weather.
We don’t have any good metrics for measuring wild ecosystems, except long term extinction rates, but there is certainly evidence that the climate is changing faster than plants and animals can move to keep up. [Union of Concerned Scientists]
The woods I love to hike in will be very different when my niece’s children try them.
But the oceans will be the worst hit. The increase in CO₂ has led to an ongoing acidification of the water which prevents many animals from forming shells. The increase in heat has lead to bleaching coral reeves and the death of many.
More subtle changes happen too. Different species respond differently to climate change, some start breeding sooner than they would normally, others do not. Thus old ecological synchronizations are lost. A predator many start to breed in the spring before its prey does, resulting in starvation of the predator and over-population in the prey.
The oceans’ food chains are being disrupted and they are becoming less productive.
In other words, species are dying off. Humans are losing their food supplies.
The Guardian says it very well: “By comparison to what it [COP21] could have been, it’s a miracle. By comparison to what it should have been, it’s a disaster.”
The world will be less beautiful in the future.
And there will be less for humans to eat.
And there will be more humans.