By Chad Kruger Reprinted from: WSU CSANR Perspectives on Sustainability In two prior posts (threats and variability), based on our research, I have argued that climate change is not likely to be a major cause for concern for agricultural production in the Pacific Northwest until at least mid-century. A little bit of warming and a […]
The observed temperature records of the US Pacific Northwest show a small, but statistically significant amount of warming of just over 1 degree F since the year 1900. A paper published in March of this year by Abatzaglou, Rupp and Mote (2014) used a multiple linear regression model to “tease out” the contributions of different influences on climate and “to apportion trends to internal climate variability, solar variability, volcanic aerosols, and anthropogenic forcing [a.k.a. human greenhouse gas emissions]”. Unsurprisingly, the finding of this study was as expected:
Anthropogenic forcing was a significant predictor of, and the leading contributor to, long-term warming; natural factors alone fail to explain the observed warming.
And, then, this little bombshell was published this week …
Jim Johnstone and Nate Mantua NOAA just published a paper in the Proceedings of the National Academy of Sciences (PNAS) using a single linear regression model to correlate sea level pressure in the NE Pacific ocean with sea surface temperatures (SST) and surface air temperatures (SAT) in the coastal PNW. Their finding?
NE Pacific circulation changes are estimated to account for more than 80% of the 1900–2012 linear warming in coastal NE Pacific SST and US Pacific northwest (Washington, Oregon, and northern California) SAT. An ensemble of climate model simulations run under the same historical radiative forcings fails to reproduce the observed regional circulation trends. These results suggest that natural internally generated changes in atmospheric circulation were the primary cause of coastal NE Pacific warming from 1900 to 2012….
Got that? In layman’s terms, they conclude that the observed 1 degree F of warming observed over the last century in the US Pacific Northwest was due to changes in wind patterns, and that those changes in wind patterns derived from natural variability not greenhouse gas emissions from human sources.
I usually don’t wade into the “controversy” regarding natural vs. human-caused warming because a) I’m not an atmospheric scientist and therefore don’t have sufficient training to interpret methodologies and b) the causal linkage between elevated CO2 and climate doesn’t really matter when it comes to evaluating the impact climate change on agriculture. We can isolate and test the sensitivity of the effects of warming, changes in precipitation and elevated CO2 on crops, livestock and hydrology regardless of the connectivity between these variables and the cause of the change (in fact, we do just that). However, because this new study raises questions regarding how climate models forecast those future variables in our region (and we do use those forecasts), I felt it was important to note that we are cognizant of this study and anxiously awaiting resolution.
Abatzaglou, Rupp and Mote have already raised concerns about the selection of the dataset used by Johnstone and Mantua for the PNAS paper. Abatzaglou, Rupp and Mote point to the large disagreement pre-1950 between available datasets on sea level pressure (see first figure here) to indicate that the use of one or more of several different data sets with the same methodology presented in the PNAS paper may actually result in a finding more in line with their own findings (Johnstone and Mantua used only the red NCAR dataset to perform their analysis).
This new “controversy” is likely to take some time to resolve itself as more studies and analyses are conducted to evaluate the inconsistency that Johnstone and Mantua have presented. That’s what should happen in science, but it doesn’t mean that we should readily discount everything we think we know. We already know that the global climate models (GCMs) don’t capture all of the critical phenomena that drive regional climate – and that GCMs might underestimate important concerns. The question this PNAS study raises is important to resolve on many levels and may be useful for improving regional climate forecasting, but even Johnstone and Manuta indicate that their finding does not change the current interpretation of expected future impacts of anthropogenic warming in the region.
The fact is that global greenhouse gas emissions are currently increasing faster than the highest Intergovernmental Panel on Climate Change (IPCC) projected emissions scenario – and if the currently assumed causal link between emissions and temperature is even half correct, we’ll still have plenty of change to manage in the future, which I’ll address in a future post.
Abatzoglou, J. T., D.E. Rupp, & P.W. Mote (2014). Seasonal climate variability and change in the Pacific Northwest of the United States, Journal of Climate, 27, 2125-2142, doi: 10.1175/JCLI-D-13-00218.1.
Johnstone, J.A. and N.J. Mantua (2014). Atmospheric controls on northeast Pacific temperature variability and change, 1900-2012. PNAS. doi: 10.1073/pnas.1318371111
One of the caveats I always state when presenting the results of our research on projected climate change impacts on PNW agricultural production is: we don’t yet know if climate change will disrupt our existing regional climate cycles. To date, the climate forecasts for our region indicate a future where climate change amplifies the current cycles – resulting in a future that is warmer and possibly slightly wetter on average, but still keeping the pattern of relatively short-cycling between wet and dry periods. These wet and dry periods rarely last for more than a couple of years.
As I’ve pointed out before, most of the climate change impacts we’ve forecasted for crop yields fall within the relative range of historic variability for PNW agriculture. We already experience a wide range of climatic variability year in and year out (particularly for precipitation), and our cropping systems and other agricultural infrastructure has evolved to help us manage that variability. A bad precipitation year (or irrigation water shortages) is still costly and challenging for farmers to manage, but for most of the region there is a measure of truth to the proverb that “it’ll be better next year” – at least from a historical climate perspective. In our projections for future climate, the expectation of continued short-lived wet-dry cycles is part of why we’ve been much less concerned about negative climate impacts on agriculture in the PNW than scientists in other regions.
One serious concern we do have though is that many scientists question how well current global climate models perform in forecasting the risk for long-term droughts. A severe drought that lasts a decade or longer would be a game-changer for PNW agriculture.
Photo: Bert Kaufmann
A new study published in the Journal of Climate (Ault et al. 2014) attempts to quantify the risks for decadal and “megadrought” (a drought of at least 30 years) by augmenting the results of climate models with the paleo-climate data record. This paleo-climate record may be a better indicator of long-term drought risk. The authors indicate that using this methodology significantly increases the risk of decadal (>80%) and megadroughts (20-50%) across much of the southwestern US and northwestern Mexico in the next century. Given the extreme nature of the current drought, I think this new insight should be extremely concerning to anyone involved in agriculture in the desert Southwest (not to mention the US food system that has become dependent on that region for a large fraction of the produce we consume).
According to this same study, the authors forecast that the risk of long-term drought in the PNW may decrease slightly; however, they still project the chances of a decadal drought in Washington, Idaho and Montana as high as 10%. I guess that’s relatively good news? While I’m not really concerned about forecasted yield changes of + or -10%, a 10% chance of a decade-long drought is not so easily dismissed.
I think it’s too early to get overly anxious about the risk of a megadrought in the PNW, but this new study demonstrates that sustained drought is a vulnerability we can’t afford to ignore. The reality is that our human experience of climate in the PNW has occurred over a remarkably short period of time and we have designed and built very elaborate agricultural systems and infrastructure based on that relatively short glimpse of climate history. It’s something we definitely need to keep an eye on.
Toby R. Ault, Julia E. Cole, Jonathan T. Overpeck, Gregory T. Pederson, David M. Meko. Assessing the risk of persistent drought using climate model simulations and paleoclimate data. Journal of Climate, 2014; 140122102410007 DOI: 10.1175/JCLI-D-12-00282.1
In a recent interview that covered the gamut of oft-cited threats to agricultural sustainability and food security (drought, food safety, energy disruption, economics, terrorism, chemical pollution, genetic pollution, impacts on pollinators, soil erosion, climate change, etc.), I was asked which threat I thought was the biggest. I was completely stumped. For every threat that came to mind as “the big one” I could come up with at least two arguments why a different threat was bigger.
The challenge in answering a question like this is that there are too many qualifiers that need to be considered. By “biggest threat” do we mean most imminent threat, the most severe threat, the threat we have the least ability to influence, or the one that we know the least about? To answer a challenging question like this, we really need a set of actuarial tables – something comparing the (likelihood of occurring) X (severity of impact) X (our ability to adapt/manage). An analysis like this simply doesn’t exist in any comprehensive and systematic way. In the absence of a way to measure the threat, most discussions on threats tend to default to individuals defending his or her favorite threat, often to the detriment of getting anything done.
The only publication I’ve ever seen that tries to quantitatively frame a set of global threats this way was a paper called “A Safe Operating Space for Humanity” published in Nature in 2009. That paper attempted to quantify environmental risks through the lens of planetary boundaries. While it was an interesting attempt at quantification, everyone I know who has read it debates whether it adequately captures or quantifies all of the environmental risks. In addition, there is the consideration that many risks to the planet are not environmental at all – and can be both human and non-human (think asteroids). Furthermore, while agriculture is certainly captured in the assessment as a source of environmental risk, this paper doesn’t actually investigate the question of risks to agricultural sustainability or food security. We really need some kind of scoping study like this for food security, but, like the Nature paper, I doubt such a study would result in findings many of us find satisfactory.
From the following article: A safe operating space for humanity. Johan Rockström et al. Nature 461, 472-475(24 September 2009) doi:10.1038/461472a The inner green shading represents the proposed safe operating space for nine planetary systems. The red wedges represent an estimate of the current position for each variable. The boundaries in three systems (rate of biodiversity loss, climate change and human interference with the nitrogen cycle), have already been exceeded.
Thinking back to the original question I was asked, the only firm conclusion that I can come to is that the threat I understand best (climate change) is probably NOT the biggest threat – at least in terms of direct effects of climate change on agriculture and food security in the Pacific Northwest. Because of my work and expertise, I feel like I have a pretty good grasp on the nature of the climate change threat and therefore feel most comfortable about my ability to quantify what the likely and probable impacts of climate change are and the extent to which agriculture can adapt to climate change in our region. To use my formula described above, climate change has a high likelihood of occurring, a moderately high severity of projected impact (especially over the long-term), but I think our agricultural systems actually have a fair amount of capacity to adapt to/manage the threat as we currently understand it.
Furthermore, forecasted climate change represents more of a “compounding effect” on other threats we already manage rather than a stand-alone threat. For instance, climate change is projected to enhance the probability and severity of drought – but drought itself is something we already deal with and that has always been a challenge to manage. Droughts that are 10-20% worse by mid-century would certainly represent an increased threat, but that seems to be more of a marginally worse impact rather than something new and devastating.
I’m certainly not saying that I think climate change is not a serious threat to agriculture and food security. It very well may be. It’s just that I’m not sure that it is the most imminent, most severe, or the threat we have least influence over. Also, I think we’re beginning to get a much better understanding of the implications of climate change for agriculture in our region, which helps empower us to plan and adapt to potential projected change. Essentially, for me it’s more of a “known known” than most other threats I can think of. I presented this very perspective in a recent presentation I gave describing our research assessments on climate change and agriculture in the region. One member of the audience clearly stated that he didn’t agree with my “rosy picture” – and in his opinion there are already so many sustainability threats that he felt climate change might not just be a compounding concern, but rather the proverbial “straw that breaks the camel’s back”.
Our disagreement may just be the difference between optimism and pessimism, but I like to think that my relative optimism in this case is the result of an increasing scientific understanding of the threat. In fact, I can say with certainty that my perspective on the relative capacity of PNW agriculture to adequately adapt to climate change has become increasingly optimistic over the past decade as our research efforts have continued to explore the threat. I do not think that we should ignore the climate threat as though it’s not serious; I just think that there is a high likelihood that there are other, “bigger” threats to our sustainability. I’m just not sure which is the biggest.
A new paper published in Environmental Science & Technology (DeLucia et al., 2014) suggests that scientists have drastically underestimated the earth’s theoretical potential to produce biomass – by as much as 2 orders of magnitude! That’s going to take a minute to wrap my mind around.
The rationale of the authors is that most analyses of global Net Primary Productivity – or NPP (the amount of biomass produced around the world annually) – assume that natural ecosystems represent the upper threshold of potential productivity. However, we know that this is not necessarily true, as varietal development, fertilizer enrichment, agronomic management, and supplemental irrigation (moving water from one part of an ecosystem to another increase water use efficiency) can all contribute to managed ecosystems (e.g. agricultural fields) that are considerably more productive than native ecosystems. Andy McGuire recently pointed out that for much of the irrigated western US, agricultural yields are much higher than would be expected given the characteristics of the soils produced by native vegetation.
But two orders of magnitude? That’s phenomenal and leaves me thinking two things:
Corn production. Photo: A. Eminov
First, I’m not sure I really want to live on a planet where we focus on maximizing global NPP. While it may theoretically be possible to see this kind of increase in productivity, such increases would likely result in challenges to sustainability of an equivalent magnitude. Many of our current agricultural sustainability concerns are caused by such things as varietal development, fertilizer enrichment, agronomic management and supplemental irrigation. For instance, biomass yields for corn in the arid west are often an order of magnitude greater than biomass productivity in shrub steppe, but we also add upwards of an order of magnitude more water and fertilizer than is present in the native ecosystem. Isolating this degree of human intervention to a few million acres in the west gives us plenty of challenges to deal with. Thinking about ocean to ocean management of our landscape should be humbling.
Second, this analysis provides the first rigorous global quantification (even if it is very simplistic) that gives some credible basis for some of the more outlandish claims for terrestrial carbon sequestration potential (e.g., Alan Savory’s grazing systems). One of the most frequent criticisms of these claims are that it wouldn’t be possible to sustain productivity increases sufficient to drive soil carbon sequestration rates long enough to achieve the change Savory and others have suggested possible. Restoring soil carbon to “native levels” has often been assumed to be the theoretical maximum. However, we know that the primary driver of soil carbon increases is biomass inputs – so even an order of magnitude more biomass produced should translate into significantly greater carbon sequestration than might currently be assumed.
Whether this “new theoretical maximum NPP” is plausible, much less desirable at a global level, it does give me pause to think about whether targeted management of certain landscapes (e.g. rangelands) do hold a much greater potential to produce biomass and sequester carbon than has been assumed to date.