Three-decade changes in greenhouse gases and average temperature

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In 2011, we wrote a column, “Global warming is happening: How should farmers respond?” ( In that column we began by saying, “There was a time when one could legitimately argue that there was a lack of scientific agreement over the issue of the role of humans in global warming and even whether we were in a cooling or warming period. It is becoming increasingly difficult to ignore the scientific evidence.”

Well, we were wrong, not about the global warming part, but rather the “increasingly difficult to ignore the scientific evidence” part. Shortly after that column appeared in print, we were contacted by an attorney for a state’s department of agriculture who demanded to know what evidence we used to support our contention that the climate change that is occurring is human induced.

We also received emails from several readers. One wrote, “It was with some degree of astonishment that I read, and have heard discussed, this latest piece about human-caused global warming. I was under the impression that the theories about mankind’s addition to the global warming trend had been thoroughly debunked.”

Well the issue of the role of humans in climate change has not gone away. In fact, with the release of the most recent report from the Intergovernmental Panel on Climate Change, the urgency of addressing the issue has become greater than ever.

Both the National Geographic’s article, “A Five Step Plan to Feed the World,” which we examined in our previous column, and the Chicago Council on Global Affairs’ publication, “Advancing Global Food Security in the Face of a Changing Climate” (—the focus of this week’ column, takes the impact of agriculture on climate change and the impact of climate change on agriculture seriously.

While the National Geographic article acknowledges both impacts, it focuses its comments on feeding a larger population in 2050 and an increasing middle class in developing countries, the publication by the Chicago Council gives more background on the issue of climate change.

The Chicago Council report, with Gerald C Nelson serving as the principal author of the report and Douglas Bereuter and Dan Glickman serving as Cochairs of the advisory group responsible for the publication, provides a definition for “weather and climate.”

In defining “weather and climate,” Nelson writes “‘Climate’ is usually defined as average weather. The United Nations Framework Convention on Climate Change (UNFCCC) defines ‘climate change’ as changes in climate caused directly or indirectly by human activity.* People do many things to cause local changes in climate. For example, ‘heat islands’ are caused by higher temperatures in cities compared to the surrounding countryside. Deforestation can cause local increases in temperature and changes in rainfall patterns. This report, however, focuses on global changes in climate.”

The asterisked footnote says, “Article 1 of the UNFCCC defines climate change as ‘a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.’”

The first section of the first part of the report is titled “A Changing Climate Will Alter the Global Food System,” and is the section that reviews the key points on climate change. They start with an idea that every farmer understands better than almost anyone else: “food production and food prices are inextricably linked to weather.”

With climate change, the likelihood of extreme weather events increases, triggering more frequent fluctuations in production and thus prices. While farmers in the US and around the world have normal variations in weather and production factored into their farming activities, an increase in extreme weather events can put their livelihood at risk.

The report provides graphs that show the increase in the atmospheric concentrations of major greenhouse gases between 1978 and 2013—carbon dioxide, 335 parts per million to 390 ppm; nitrous oxide, 340 parts per billion to over 390 ppb; methane, over 1550 ppb to over 1800 ppb. Over that same period, the average global temperature has increased by 1 degree. They also point out that “unlike other major greenhouse gases that disappear from the atmosphere relatively quickly, carbon dioxide stays put for hundreds to thousands of years, making increased concentrations in the atmosphere difficult to reverse.”

Agricultural activity is responsible for 24 percent of greenhouse gasses that contribute to global warming. The biggest contributor is the conversion of grasslands and forests to agricultural production. “Without careful management practices, soils in the newly converted lands lose about 50 percent of the initial soil organic carbon in the top surface layer in 25 to 50 years in temperate climates and in five to 10 years in the tropics, making land less productive.” Other contributors include digestion and decomposition of manure from ruminants, rice production, improper use of fertilizers, and farm machinery that burns fossil-based fuels.

As average global temperatures increase, the zones in which crops are grown will for the most part move toward the poles or to higher elevations—there is a limit to both moves. One only has to look at the northward march in US corn production to understand this. In addition, the areas with comparative advantage in crop production will be partly determined by changes in rainfall and rainfall patterns. Too much rain at the wrong time can be devastating while drier weather at harvest can be beneficial.

They point out that for most countries, between 1980 and 2008 climate change has had a negative impact on crop yields. In addition to yield drag, farmers will face increased problems from plant diseases and pests, both domestic and invasive. As any temperate farmer can attest, cold winters reduce pest pressure while warmer winters allow them to survive in greater numbers. With climate change, the winters will generally be warmer.

Although it has been less studied than yield and production, climate change also has a negative impact on the quality of the food that is produced. Wheat protein levels fall at high carbon dioxide levels. In addition, “experiments in the United States and China have shown that in nonleguminous grain crops, protein and mineral content such as iron and zinc are substantially reduced when carbon dioxide concentrations reach levels likely to occur by midcentury.”

Livestock production will be negatively impacted as animals face increased heat stress. Higher temperatures also affect fertility. Higher temperatures will negatively affect the nutritional content of forages, they argue.

For farmers whose fields are only slightly above the average sea level, any increase in that level can be devastating, either by flooding or salt-water intrusion into fresh water aquifer. Some island states will be submerged by a rise in the sea level.

And if this is not challenging enough for farmers, the report says that transportation costs will increase because “higher temperatures reduce the efficiency of human and animal transport, require roads to be built to higher standards, and increase the costs of cooling for sensitive produce.”

Next week we will look at their argument that “Adapting the global food system to climate change should be a priority.”

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Brin Jenkins    
Cornwall UK  |  June, 18, 2014 at 11:50 AM

There is no evidence, and the CO2 theory is debunked. Here in the UK we could do with a bit of warming its colder than any time in the last 60 years. Now is the best Summer we have had for many years and tomatoes are still slower in developing compared to the mid 70's. Lets see some real peer review not re-mustered economists and statisticians. Many Physicists don't agree with the PC hype.

California  |  June, 19, 2014 at 10:50 AM

Please provide evidence that the CO2 theory is debunked.

Douglas Grenfell    
London, UK  |  June, 18, 2014 at 01:51 PM

Smoke and mirrors plus a dodgy computer programme is the only proof we've had from scientists along with governments that see global warming as an easy way to raise extra taxation which they can then spend trashing the countryside and now the sea views. Why they cannot admit that while it may be warming up we have just finished a mini ice age and that this process is the norm for Earth Get used to it.

Wyo  |  June, 18, 2014 at 04:38 PM

What a travesty that university extension agents would use their time for advancing a liberal socialist agenda. Not much better that a "cattle" entity would publish it.

SD  |  June, 18, 2014 at 05:05 PM

Forget “Global Warming”, it enables manufactured controversy evoking "uniformly warmer climate” seemingly contradicted by unseasonable cold weather. “Man-made Climate Change “ leads to questions like “Hasn't climate always changed?” Couldn’t Man Made Climate Change” be good? Isn't it a future issue? Measurements indisputably document that humans cause non-uniform changes in atmospheric composition, chemistry and radiation linking to levers affecting physical weather forcing,tipping the balance of weather creating sporadic, nonlinear shifts transforming normal weather events like thunder storms into killer storms spawning larger hail, floods and killer tornadoes. Normal weather patterns evolve into extreme cold snaps, untimely frosts, shriveling heat waves and damaging winds. Farmers and ranchers, on the front lines of the effects and the cure, suffer staggering economic losses. Only agriculture can store greenhouse gases in the soil in forms that benefit productivity, and buy time while increasing the resilience of our food supply to Climate Chaos –an unquestionable and growing reality. What can we do? First we must not remain gullible pawns of the economic beneficiaries of doing nothing, while spewing misinformation and disregarding future costs to farmers, ranchers and society. Second, we must slow down Chaotic Climate forcing while developing effective coping strategies. Policy can’t regulate weather but can reward agriculture for implementing landuse practices that buy time and increase resilience. Third, we must balance short-term economics against long-lasting impacts on Climate Chaos. Fourth, we must invest in scientific and infrastructure enhancing forecasts and planning.Climate Chaos is here and accelerating.

Berkshire, England  |  June, 20, 2014 at 06:58 AM

Hello John in California. It should not be incumbent upon non-believers (of anything!) to provide evidence. It is ALWAYS necessary for those making a statement to provide evidence for their belief - and this is where the theory behind man-made global warming comes tumbling down, as there is no evidence! What we think we know about CO2 theory should mean that warming occurs. The problem is that the theory is quite evidently incorrect. During the past 15 years the atmosphere has undergone massive forcing from CO2 (if the theory were correct) which should have resulted in significant warming. I'm sure you know that there hasn't been any! We only 'know' what CO2 does in a computer model, and that model must be wrong. When the observation doesn't fit the data, the data is wrong. That is very, very simple. So John, the theory is debunked by observation. Observation is evidence, John. I say very clearly to you; if you believe that CO2 DOES result in warming, show us your evidence. Of course, I know you don't have any. The beauty of the debate is this: If we had evidence to that effect then none of us would be arguing about it! But the very FACT that no evidence exists that links man-made emissions of CO2 to a warming of the atmosphere means that we can argue about it. QED.

UK  |  June, 20, 2014 at 08:26 AM

Baz, ignornig evidence is not the same as there being no evidence.

Denver  |  June, 20, 2014 at 12:16 PM

From wikipedia if you search species extinct. "It is estimated that over 99.9% of all species that ever lived are extinct". I suspect if climate remained stagnant that would be the biggest climate change the earth has ever experienced.

Berkshire, England  |  June, 20, 2014 at 02:09 PM

Al, if you have evidence, then please state it - but of course, I know you haven't. All you have is a physics theory of how CO2 reacts in the atmosphere. But, then again, you KNOW that climate science is THE most chaotic science there is, and we haven't a clue what feedbacks we input stuff into computer models. But theory and computer models aren't evidence Al...and you know it.

SD  |  June, 23, 2014 at 12:42 PM

You climate deniers are disingenuous or just foolish (most likely both). Of course climate changes. Normally, except for huge asteroid impacts or enormous volcanoes that happen every 100 million years or so, the changes we have experienced over a couple of decades, normally take place over about 100,000 years or so. We know the sources of Greenhouse gases (GHGs). We know what wavelengths of energy they absorb. We have been accurately measuring the changing concentrations. So we know the amount of climate forcing that is occurring due to humans. The rest is just details. Scientists continue to refine our understanding of important climate-system feedbacks. No one can make a credible argument that the GHG concentrations are not rapidly changing nor can they assert that these chemical species are not radiatively –active. We must be concerned about the climate chaos that is happening now regardless of the cause. Preparing for the effects, slowing it down and improving the scientific infrastructure to make better predictions of extreme weather events will save money and lives now and make the future more survivable for our Grandchildren.

Craig A. Moore    
Billings, MT  |  June, 24, 2014 at 10:14 AM

PZ is like many deriding people that are not following the governments reasoning. No PZ, we are not denying climate change as we know it has, is and always will. We are questioning the "scientific" theories, and that is exactly what they are to this point. They refuse to look into solar activity and the effects of the Earths magnetic effects on the climate. Why?

SD  |  June, 24, 2014 at 12:17 PM

Gravity is a theory. So is Relativity. Both are extremely useful predictors. Drop a water glass, theory accurately predicts speed and force. We can argue the details, but models of how gravity works tell us that if the glass is dropped from great height onto a sidewalk, it is likely to break. Genetic theories predict outcomes of animal breeding. We base most of our plans on theories. .The physics and chemistry of climate forcing have nothing to do with “the Government’s reasoning”. Climate deniers attempt to confuse with uninformed detail. Of course Milankovitch cycles, solar flares and thousands of additional physical factors that can affect LONG TERM climate cycles have been thoroughly examined and are included in climate models. But basic facts of climate science are as simple as the “falling glass” example: The composition of the atmosphere has changed dramatically in a few decades. With no shifts in behavior, changes will accelerate. The basic physical and chemical impacts—absorption spectra, reaction rates, global distributions are accurately measured. If we put these gases in a vessel exposed to sunlight we can accurately predict the temperature change. The rest is just detail. We are experiencing what theory predicts and geologic history documents. Climate Chaos precedes shifts in climate equilibrium. Farmers and ranchers are the bellwether. While pointlessly debating if Climate Chaos is human-caused, ( as confirmed by many independent lines of evidence) the reality is that we can only effectively influence human factors accelerating Climate Chaos. It is ironic that victimized farmers and ranchers align with increasingly-wealthy beneficiaries at the expense of their own and their children’s futures.

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