The benefits of carbon dioxide
作者：Matt Ridley @ 2015-10-20
Global greening may save more lives and forests than warming costs
My Times Column on the surprisingly large benefits of carbon dioxide emissions:
France’s leading television weather forecaster, Philippe Verdier, was taken off air last week for writing that there are “positive consequences” of climate change. Freeman Dyson, professor emeritus of mathematical physics and astrophysics at the Institute of Advanced Study in Princeton, declared last week that the non-climatic effects of carbon dioxide are “enormously beneficial”. Patrick Moore, a founder of Greenpeace, said in a lecture last week that we should “celebrate carbon dioxide”.
Philippe Verdier，法国电视天气预报员中的佼佼者，因写到气候变化具有“积极效应”而于上周被调离播报岗位。Freeman Dyson，普林斯顿大学高等研究院数学物理学和天体物理学荣休教授，上周称，二氧化碳的非气候影响“极为有益”。Patrick Moore，绿色和平组织创始人之一，在上周的一次讲座中说，我们应该“为二氧化碳而欢庆”。
Are these three prominent but very different people right? Should we at least consider seriously, before we go into a massive international negotiation based on the assumption that carbon dioxide is bad, whether we might be mistaken? Most politicians today consider such a view to be so beyond the pale as to be mad or possibly criminal.
Yet the benefits of carbon dioxide emissions are not even controversial in scientific circles. As Richard Betts of the Met Office tweeted last week, the “CO2 fertilisation effect” — the fact that rising emissions are making plants grow better — is not news and is discussed in the reports of the Intergovernmental Panel on Climate Change.
The satellite data show that there has been roughly a 14 per cent increase in the amount of green vegetation on the planet since 1982, that this has happened in all ecosystems, but especially in arid tropical areas, and that it is in large part due to man-made carbon dioxide emissions.
Last week also saw the publication of a comprehensive report on “Carbon Dioxide — the Good News” for the Global Warming Policy Foundation by the independent American scientist Indur Goklany, to which Freeman Dyson wrote the foreword. The report was thoroughly peer-reviewed, as was almost all of the voluminous literature it cited. (Full disclosure: I helped edit the report.)
上周，更有一份关于“二氧化碳——大好消息”的很全面的报告出炉，这是由美国独立科学家Indur Goklany向全球变暖政策基金会（GWPF）提供的，并由Freeman Dyson作序。该报告经过了充分的同行评议，报告所引用的巨量文献也几乎全都如此。（大曝光：我参与编辑了该报告。）
11 Goklany points out that whereas the benefits of carbon dioxide are huge and here now, the harms are still speculative and almost all in the distant future. There has so far been — as the IPCC confirms — no measurable increase in droughts, floods or storms worldwide, no reversal in the continuing rapid decline in deaths due to insect-borne diseases, and no measurable impacts of the continuing very slow rise in global sea levels.
In stark terms, Bangladesh is still gaining land from sedimentation in its rivers’ deltas, has suffered no increase in cyclones, but has benefited from reduced malnourishment to the tune of billions of dollars from higher crop yields as a result of carbon dioxide emissions.
[This is the summary from Goklany’s report:
1. This paper addresses the question of whether, and how much, increased carbon dioxide concentrations have benefited the biosphere and humanity by stimulating plant growth, warming the planet and increasing rainfall.
1. 本论文讨论了升高的二氧化碳浓度 是否以及多大程度上，以刺激植物生长、暖化地球、增加雨量的方式，使生物圈和人类受益。
2. Empirical data confirms that the biosphere’s productivity has increased by about 14% since 1982, in large part as a result of rising carbon dioxide levels.
3. Thousands of scientific experiments indicate that increasing carbon dioxide concentrations in the air have contributed to increases in crop yields.
4. These increases in yield are very likely to have reduced the appropriation of land for farming by 11–17% compared with what it would otherwise be, resulting in more land being left wild.
5. Satellite evidence confirms that increasing carbon dioxide concentrations have also resulted in greater productivity of wild terrestrial ecosystems in all vegetation types.
6. Increasing carbon dioxide concentrations have also increased the productivity of many marine ecosystems.
7. In recent decades, trends in climate-sensitive indicators of human and environ- mental wellbeing have improved and continue to do so despite claims that they would deteriorate because of global warming.
8. Compared with the benefits from carbon dioxide on crop and biosphere productivity, the adverse impacts of carbon dioxide – on the frequency and intensity of extreme weather, on sea level, vector-borne disease prevalence and human health – have been too small to measure or have been swamped by other factors.
9. Models used to influence policy on climate change have overestimated the rate of warming, underestimated direct benefits of carbon dioxide, overestimated the harms from climate change and underestimated human capacity to adapt so as to capture the benefits while reducing the harms.
10. It is very likely that the impact of rising carbon dioxide concentrations is currently net beneficial for both humanity and the biosphere generally. These benefits are real, whereas the costs of warming are uncertain. Halting the increase in carbon dioxide concentrations abruptly would deprive people and the planet of the benefits of carbon dioxide much sooner than they would reduce any costs of warming.]
It is worth remembering that commercial greenhouses buy carbon dioxide to enhance the growth of plants, so the growth responses are well known — and it’s not until carbon dioxide reaches five times current concentrations that the benefits level out. As Patrick Moore pointed out, those were normal levels for much of earth’s history.
In addition, hundreds of “free-air concentration experiments” have measured how much increased carbon dioxide levels enhance crop yields in open fields. So it is fairly easy to work out how much carbon dioxide emissions are helping world agriculture: by about $140 billion a year, or $3 trillion in total so far. If reparations are to be paid, perhaps farmers should pay coal producers (full disclosure: I’m both).
Actually, this may be an underestimate: experiments show that crops tend to benefit more than weeds (most crops have a more responsive kind of photosynthetic machinery called C3, while weeds mostly have a less responsive kind called C4).
Increased carbon dioxide enhances drought resistance in plants, benefiting dry regions such as the Sahel, which has greened significantly in recent decades. And Goklany calculates that we need 11-17 per cent less land for feeding the world than we would if we had not increased carbon dioxide levels: so emissions have saved — and enhanced the growth of — a lot of rainforest.
[Here’s one weed experiment, as described in Goklany’s report:
“A Chinese experiment tested this idea by enriching carbon dioxide levels over plots of rice to almost twice the ambient level. This enhanced the ear weight of the rice by 37.6% while reducing the growth of a common weed, barnyard grass, by 47.9%, because the faster-growing rice shaded the weeds. Figure 1 illustrates the differing responses to elevated carbon dioxide concentrations of rice, a C3 plant, and the green foxtail Setaria viridis, a grass some- times proposed as a genetic model system to study C4 photosynthesis.”]
[For instance a study published last week found the following:
Since 2012, the researchers have pumped extra CO2 into three of six basketball court-sized rings of 80-year-old bush. This has raised the CO2 concentration in the three plots to about 550 parts per million, up from the ambient level of 400 ppm. Measurements revealed that for each unit of water absorbed, the trees in the CO2-enriched rings reaped 35 per cent more carbon than the trees in the control plots.]
Well, all right, but surely the climate harms will one day outweigh the growth benefits? Not necessarily.
At the moment, impacts from the modest warming we saw in the 1980s and 1990s are also positive: slightly fewer premature deaths, which peak in cold weather more than in hot weather, slightly longer growing seasons and so on.
A paper published last week concludes that if the world does warm significantly, China’s rain systems will shift north, increasing rainfall in the dry north and reducing flooding in the hot south.
Besides, human adaptation means we can capture the benefits and avoid the harms. The IPCC’s forecast warming range includes the possibility that we will still be enjoying net benefits by the end of the century, when the world will (it says) be three to 16 times richer per capita. The fastest way to cut deaths from bad weather today (such as the storm that just battered the Philippines) is to make people richer, not to make weather safer: we have already cut world death rates from droughts, floods and storms by 98 per cent in the past century.
As Goklany demonstrates, the assessments used by policy makers have overestimated warming so far, underestimated the direct benefits of carbon dioxide, overestimated the harms from climate change, and underestimated the human capacity to adapt.
Well, what about the ocean? Here too there’s good news. More carbon dioxide means faster growth rates of photosynthesisers in the sea as well as on land, an effect that is being observed in algae, eelgrasses, corals and especially plankton, such as the abundant creatures known as coccolithophores, whose biomass has increased by 40 per cent in the last two centuries.
[This is what the authors said about coccolithophores:
“Here, we present laboratory evidence that calcification and net primary production in the coccolithophore species Emiliania huxleyi are significantly increased by high CO2 partial pressures. Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40% increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate.”]
That’s not to say coral reefs and fisheries are not in trouble — they are, but because of pollution, overfishing and run-off, not carbon dioxide. The tiny reduction in alkalinity (misleadingly termed “acidification”) caused by dissolved carbon dioxide is potentially negative in the distant future, but has been much exaggerated — as a big review of 372 studies has concluded. One recent experiment with a common Caribbean coral found that rising carbon dioxide levels would have no impact on its ability to build reefs for several centuries, while modest warming would actually help it slightly.
[This is what that meta-analysis concluded from a comprehensive survey of all studies:
“In summary, our analysis shows that marine biota is more resistant to ocean acidification than suggested by pessimistic predictions identifying ocean acidification as a major threat to marine biodiversity (Kleypas et al., 1999; Orr et al., 2005; Raven, 2005; Sponberg, 2007; Zondervan et al., 2001), which may not be the widespread problem conjured into the 21st century. Ocean acidification will enhance growth of marine autotrophs and reduce fertility and metabolic rates, but effects are likely to be minor along the range of pCO2 predicted for the 21st century, and feedbacks between positive responses of autotrophs and pH may further buffer the impacts.”]
With tens of thousands of activists and bureaucrats heading for a UN conference in Paris next month, there is such vast vested interest now in demonising carbon dioxide that it will be hard to change the world’s mind. Freeman Dyson laments that “scientific colleagues who believe the prevailing dogma about carbon dioxide will not find Goklany’s evidence convincing”, but hopes that a few will try. Amen.
[Dyson went on:
“That is to me the central mystery of climate science. It is not a scientific mystery but a human mystery. How does it happen that a whole generation of scientific experts is blind to obvious facts?
…Indur Goklany has assembled a massive collection of evidence to demonstrate two facts. First, the non-climatic effects of carbon dioxide are dominant over the climatic effects and are overwhelmingly beneficial. Second, the climatic effects observed in the real world are much less damaging than the effects predicted by the climate models, and have also been frequently beneficial.
I am hoping that the scientists and politicians who have been blindly demonizing carbon dioxide for 37 years will one day open their eyes and look at the evidence.
Goklany and I do not claim to be infallible. Like the climate-model experts, we have also evolved recently from the culture of the cave-children. Like them, we have inherited our own set of prejudices and blindnesses. Truth emerges when different groups of explorers listen to each other’s stories and correct each other’s mistakes.”]
This column produced a lot of commentary. In response to one especially misleading article in the Guardian, Indur Goklany made the following point:
Your correspondent, Mr. Nuccitelli, hasn’t read with sufficient care the GWPF report he is criticizing. Had he done so, he would have known better than to present the figure from the IPCC of estimated crop yields through the year 2109, or repeat Dr. Betts’ claim that studies on crops include CO2 effects, without noting that the vast majority of crop studies did not, in fact, consider CO2 effects. Specifically, the GWPF report (at page 29) notes:
The IPCC AR5 synthesis of modelled estimates of the impact of recent climate trends on yields for major staple crops notes, in a remarkable understatement, that ‘[s]ome included effects of positive carbon dioxide trends…but most did not’ (Ref. 175). In fact, only 2 of 56 studies considered carbon dioxide increases (Ref. 176). For this reason alone the IPCC’s claim that the impacts of global warming to date on agricultural productivity and food security are likely negative is suspect.
References 175 and 176 (within the quote) both refer to the IPCC AR5 WGII’s chapter 7 (on Food Security and Food Production Systems), page 492, Figure 7–2. Ref. 176 also notes that “Remarkably, according to Figure 7–2, the studies that considered carbon dioxide suggest that the carbon dioxide effect reduces yields.” To put that into plain English, these studies, or their interpretations, are not credible.
Note that the figure on future crop yields presented in Mr. Nutticelli’s article draws from Figure 7-2 referred to in the foregoing.
The GWPF report also notes that impact assessments in general and crop studies in particular:
1. Employ scenarios that overstate warming rates by anywhere between 2- to 4-fold. Even the IPCC has noted the tendency of models to exaggerate the rate of warming. See pages 24-25 of the GWPF report, and p. 769, Chapter 9, IPCC AR5 WGI. This matters for two reasons. Firstly, the world is unlikely to be as warm as projected by the IPCC’s scenarios. Secondly, the lower the rate of warming, the lower the magnitude of negative impacts.
2. Do not fully account for technological change that ought to occur between now and 2109 (the date used in your correspondent’s figure), which would reduce the net negative impacts of climate change while simultaneously making it easier to adapt to them.
2. 没有充分考虑到从今至2109年间（贵刊记者的数据中所用日期）肯定会发生的技术变革 ，而这些技术变革将会在减少气候变化净负面影响的同时，使得适应它们变得更容易。
For all these reasons the IPCC’s estimates of future impacts are prone to large overestimates, and the figure presented by your correspondent is suspect, to put it mildly.