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Our planet is changing. Increased levels of carbon dioxide (CO2) in our atmosphere and rising global mean temperatures will definitely bring changes for gardeners. However, in the short term, you can prepare for and manage these changes.
To adapt to climate change, you have to understand it. For gardeners, atmospheric CO2 levels and the global mean temperature, or the average of temperatures all over the globe, are the most relevant data. In the million years prior to the Industrial Revolution, the average level of atmospheric CO2 was 280 parts per million (ppm), as determined by ice core samples and marine sediment testing. CO2 levels climbed past 300 ppm in the early 20th century and continued to rise. When scientists at the Mauna Loa Observatory in Hawaii began recording levels of atmospheric CO2 in 1958, their readings averaged 315 ppm, with peaks about 4 ppm above average in May, and valleys about 4 ppm below average in November. By 2015, the average level of CO2 in our air reached 400 ppm. In 2019, the average was 415 ppm. So, there’s now roughly 50 percent more CO2 in our atmosphere than there was just 250 years ago.
CO2 levels in the deep past also fluctuated, and at times were much higher than the present day. Back in the Cambrian Period, for example, CO2 exceeded 4,000 ppm. Of course, the flora and fauna of that time were adapted to those conditions, and CO2 levels have never before changed as quickly as they are now.
Carbon dioxide is two oxygen atoms (the “dioxide” part) attached to a carbon atom. Molecules of carbon dioxide absorb energy from light rays and thus trap heat that would otherwise dissipate into space. A certain amount of atmospheric CO2 is necessary for life as we know it, but rapidly increasing levels of CO2 result in an equally rapid increase in the global mean temperature. Scientists project that the global mean temperature will rise by 3.6 to 7.2 degrees Fahrenheit by the year 2100.
Is It Really Getting Hot in Here?
In 2017, the global mean temperature was 58.6 degrees. This is about 1.8 degrees higher than the global mean temperature in 1880. For perspective, the highest recorded temperature on Earth was 134.1 degrees in July of 1913 in Death Valley, California. The lowest was -129 degrees in July of 1983 at the Vostok Ice Station in Antarctica. Gardening would be impossible at these extremes, but it’s straightforward at the global mean temperature.
The global mean temperature doesn’t change with the seasons; when it’s summer in North America, it’s winter in Australia, and the global mean incorporates those temperatures at the same time. Change in the global mean temperature also isn’t evenly dispersed over Earth. The poles are expected to warm more quickly than equatorial regions. It’s also important to understand that temperatures are trending higher in the long term — they aren’t necessarily getting higher every day.
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In addition to seasonal cycles of heat and cold, there are 20-year cycles of global heating and cooling, which we’ll continue to experience. However, all these ups and downs will end up a little higher in the long run. Think of a graph of a sine wave, and then tilt the right end of the X-axis up slightly. That’s the model of how the Earth will warm this century, with ups and downs, but an overall upward trend.
Global warming will cause a number of changes, including rising sea levels, thawing polar permafrost, an earlier average arrival of spring, and a later average arrival of winter. The Zones where various crops can best be grown will move slightly toward the poles. The French, for example, are worried that the best wine-growing regions on Earth may be in Germany in a couple of decades. And the variability in weather will increase, along with some seasons that produce a larger-than-average number of storms. The variability in weather, not the temperature change, will have the most impact on gardeners.
Early Springs and False Hopes
Every avid gardener knows the average last frost date in their area. We watch weather forecasts, plan our gardens, and hope to start getting seeds or transplants in the ground soon after. As our climate changes, average last frost dates will come sooner in the year, but this will be a slow, variable process. Some years, we’ll be surprised by a very early, warm spring, while overly late frosts set us back in other years.
Smart gardeners will be aware, as they always have been, that the first few warm days of the year aren’t necessarily a sign that it’s time to start gardening. However, with a little planning, gardeners can take advantage of early springs when they occur and reduce the risks associated with late frosts. Two approaches in particular that may help deal with variable early spring weather are starting seeds indoors and using row covers or cloches in your garden.
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If you see potential to begin planting early, consider starting some of your plants indoors. If you plant in containers larger than the average 4-well nursery flat, you can keep the plants inside longer, if need be. Square 4-inch planters are fairly cheap, and most garden vegetables won’t outgrow them for a couple of weeks after sprouting. You could, for example, plant so your vegetables sprout a week or two before your last frost date. Then, if spring arrives early, you can transplant early. If spring arrives at its usual time — as it often will — you can still plant the seedlings.
Row covers and cloches allow gardeners to elevate soil and air temperatures a bit, which protects tender plants from frosts. They’re essentially little greenhouses. As climate change continues to unfold, and spring weather becomes more variable, these will be increasingly valuable. Row covers or cloches will allow you take advantage of early springs while mitigating the risks of cold snaps.
Many garden vegetables’ fruit set is temperature-dependent. Most tomatoes, for example, won’t set at temperatures above 95 degrees. As such, if you live in an area with high summer temperatures, getting vegetables into your garden early enough to flower before the hottest part of summer is important. With the expected increased variability in weather, you may need to seed or transplant plants as early as possible in warmer-than-average years.
Late Winters and Mixed Opportunities
Just as spring will, on average, arrive sooner, winter will, on average, arrive later. The phrase “on average” is important, because — as with spring — variability will be the primary concern. Later winters give cool-weather crops extra time to mature.
Like dealing with variable spring weather, row covers or cloches can protect plants from unexpected freezes and extend the fall gardening season substantially. Vegetables that produce continually can be shepherded along until the first hard freeze. To give one example, Brassica plants — including cabbage, broccoli, cauliflower, turnips, etc. — will deal well with cooler fall temperatures.
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In regions that typically have mild winters with few hard freezes, unusually warm winters may lead to spring insect problems. In North America, northern regions typically have enough hard freezes to kill many of the insects buried in the soil, but mild winters leave these insects to emerge in spring. For example, in Colorado, more mountain pine beetles have been surviving in recent years, causing greater problems in pine forests. Climate change will gradually expand the regions that don’t have hard freezes, but the transition will be variable.
If you’re faced with an unexpectedly buggy season, you have many management options. My favorite approach is to plant tall native plants around the garden. These will serve as perches for insect predators (as well as an attractant for pollinators). I typically accept a small number of garden pests as the cost of maintaining a healthy insect predator population (see “Boost Biodiversity with Regenerative Agriculture” [link] for more regenerative agriculture techniques). Hand-picking large insects is easy in the early morning, when they’re slowed by lower temperatures. If an infestation gets out of hand, I’ll deadhead the plant, spray it with a synthetic pesticide, and then drape it with netting. This will kill the pests; removing the blooms will prevent the pesticide from affecting pollinators or insect predators.
Irregular Rainfall, Storms, and Temperatures
Variable weather patterns will affect the amount of rainfall a region experiences and the intensity of storms.
If you receive less rainfall than usual, the solution is obvious — just water or choose drought-resistant plants. However, unexpectedly rainy seasons can cause multiple problems in a garden. If your garden doesn’t drain well, standing water can kill plants. Amend garden soil with sand, and landscape to allow excess water to drain away. A wet garden can also develop problems with fungi, especially during warm spells. Space plants so air can flow between them to deter fungi. Fungicide will help if plants are affected, and early applications of fungicides are more effective than waiting until the problem is advanced.
High winds can damage gardens. Tall plants, such as corn, can lodge, and trellises can blow over. Most of the time, plants that topple in a storm will right themselves. Sometimes, the gardener may need to help by freeing their leaves and rinsing them off. Wind damage can be mitigated by windbreaks — another good use of sturdy native perennials — and strong trellises.
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We used to call climate change “global warming,” and you might think heat would be the biggest problem facing future gardeners. However, the global mean surface temperature is expected to be 62.2 to 65.8 degrees by the end of the century. Overall, the variability in weather resulting from this rise in temperature — combined with unusual weather patterns — will cause local heat waves and cold snaps.
Warmer-than-usual weather will mean more frequent watering; however, fungi thrive in heat and moisture. Set up a drip watering system or water with a soaker hose to apply water directly to the soil. It’s less wasteful than overhead watering and will limit fungal growth.
There’s no easy remedy for unusually cold weather in the peak of summer. If temperatures get low enough, row covers may help, but you’ll have to ride out moderately cool temperatures. Most plants that develop better in warm temperatures will be fine if they get enough sunlight.
Plan for Everything
In the future, planning your garden will be a lot like it’s always been. After all, the average difference between what you’ve experienced in the past and what’s expected in the future is relatively small. The amount of change depends on how much CO2 is released in the atmosphere. Of course, despite the small average change in temperature for North American gardeners, climate change will lead to very serious changes everywhere, and especially near the poles. It’s the variability in weather — something that’s already becoming an issue worldwide — that’ll be a problem.
Global climate change won’t eliminate regional weather patterns, such as El Niño and La Niña. Consult your long-term weather forecast when you begin planning your garden. As spring nears, continue to keep an eye on forecasts. And, of course, build some flexibility into your plans.
Be prepared to move your planting days up or back, depending on the forecast — and have your equipment for cold protection ready in case it’s needed. Install drip watering, or test your existing system, and plant drought-tolerant cultivars to improve your chance of success if a dry season is forecast. If a wet season is forecast, amend the soil or landscape to improve drainage and runoff. A little extra forethought and planning will pay big dividends if you have unusual weather. If you prepare each year for the worst, most years will be a pleasant surprise.
Chris Colby is a scientist, writer, homebrewer, gardener, and contributing editor of Beer and Wine Journal. He lives with his wife and cats in Bastrop, Texas.