Climate change? Show me evidence (Viewpoint)

by | Nov 20, 2017


(Editor’s note: Dr. Sara Via is a professor and climate Extension specialist with the University of Maryland-College Park. She can be reached at

If you’re not sure whether climate change is real, you’re not alone.
Although recent surveys reveal that 75 percent of Marylanders think climate change is occurring, many people say they just don’t know enough to be certain about whether it is a problem.
It’s not surprising that people are confused.
Climate change isn’t always taught in schools and it wasn’t taught at all when today’s adults were school kids.
We can’t rely on personal experience for evidence, because variability in weather makes it hard to detect climate trends in real time.
Our friends and neighbors might not know any more than we do.
And the recent injection of political opinion into the climate discussion has only added to the confusion by distracting people from reliable scientific evidence.
So, what does the evidence say about some common climate change questions?
1. The climate is always changing and farmers adapt. How is this any different? Farmers are experienced in dealing with dramatic fluctuations in weather. However, climate change involves trends that go far beyond the kind of unpredictable weather we’ve had in the past. For example, fourteen of the fifteen hottest years since 1885 have been after 2000 and even adjusting for inflation, the six years with the most billion-dollar disasters have all been since 2008. From 1951-1980, about one in a thousand summer days could be classified as extremely hot. Now, one in ten days are that hot. Compared to 1950, temperature and rainfall records for Maryland show more days over 100 degrees, more nights over 80 degrees, more rain in spring and fall, and hotter dryer summers. These changes are occurring very quickly compared to past environmental change. Adapting to this “new normal” is likely to require some new strategies.
2. There is too much uncertainty about the climate for me to make any big changes. Why worry until the scientists agree? Only 55% of Marylanders think that scientists agree about climate change. Actually, 97-98 percent of scientists with expertise in climate-related issues agree that climate change is real because so many bits of independent evidence are consistent. In science, every idea is tested repeatedly and scrutinized by other scientists who question whether it’s wrong or incomplete. The scientific evidence on climate change is reliable because it has survived years of such rigorous review.
3. If climate change is occurring, it must be good because yields have been increasing for decades. Better technology, improved seeds and more irrigation drive yield increases in the US. One recent study of climate change and agricultural productivity shows that as of 2010, the changes in average temperature and rainfall in the United States have been small compared to other nations. This has allowed climate impacts on average productivity to be outweighed so far by superior agricultural technology. However, large regional differences in climate impacts have reduced local agricultural productivity, as seen in the prolonged California drought or areas impacted by the recent hurricanes. In other countries, where average temperatures and drought frequency have increased substantially, yields of corn and soybeans have dropped 5 percent or more.
4. Isn’t more carbon dioxide good for plants? The rising concentration of carbon dioxide in the atmosphere from burning fossil fuels is the main cause of climate change. Because plants use CO2 in photosynthesis, more could be a bonus if everything else stayed the same. However, the evidence shows that as CO2 levels increase, so does the average summer temperature and the risk of drought. Because plants reduce photosynthesis when soil moisture is low, more CO2 usually provides no benefit.
5. Why worry about the temperature increasing a few degrees? We see temperature swings much bigger than that all the time. Even large temperature fluctuations tend to cancel out over time, with little impact on the average global temperature. However, adding a few degrees to the average increases extreme temperatures and causes damaging heat waves to last longer, which can substantially reduce yields.
6. I’m looking forward to when Maryland’s climate is like Georgia’s is now. It is true that temperatures in Maryland will probably rise to those currently found in Georgia, but don’t expect Georgia’s current climate or yields. The evidence shows that temperature is part of a package deal in climate change. The balmy temperatures of Maryland’s future will be very different from Georgia’s current climate, with more heat waves, more severe storms, more flooding, higher risk of drought and increasingly salty coastal soils.
Noticeable impacts of climate change on Mid-Atlantic agriculture are just beginning.
This is the time to prepare by increasing the use of “no-regrets” strategies that will help no matter what happens.
These include expanding Maryland’s leadership in no-till, making cover crops work harder, building the soil, adding irrigation and drainage and using decision support tools to increase the efficiency of water, fertilizer and pesticide applications.
(Editor’s note: The writer welcomes comments at

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