I just wrote this rather long comment on Fern’s blog, in response to her post on climate change. I really love her blog and don’t mean to sound critical, but I thought it was worth repeating here, because her comments reflect a common misconception about how scientists are investigating climate change. Often people look at one year or one season’s weather and notice it is cooler than the previous year and so conclude that there isn’t clear evidence of climate change. The problem with this is that you can look at 1 or 2 years or even 3-5 years and find evidence for or against climate change.
There is a big difference between observing the weather and measuring the climate. I understand why many people, including some scientists are still not sure, but it’s important to talk about why so many scientists are convinced. Weather in individual places over time might be warmer or cooler year to year or season to season–there are always those types of variations. What makes many scientists worry is the changes in average temperatures world wide, over decades.
Biologists are also finding many plants and animals that are changing their ranges or flowering earlier. As gardeners, we can and should be helping to gather evidence about climate change in our local areas. Some gardeners regularly monitor the weather, including daily highs and lows, rainfall, and the first and last frosts of the year. This is the kind of information that, if it’s continuous for decades, lets you begin seeing climate change in action. You can also monitor your garden plants for changes in seasonality. If you want to monitor climate change for yourself and help scientists you could join the National Phenology Network. Their volunteers have been monitoring the dates of flower blooms (lilac and honeysuckle since 1956). It’s normal to see flowers bloom earlier one year and later another, but when you monitor for decades and the average bloom date gets earlier and earlier, that’s when scientists start to worry.
It’s common for people to look at year to year variations and wonder where the evidence is, but a climate scientist is looking at decades (for temperature and precipitation changes) or centuries (if they are looking a CO2 levels in frozen ice.)
Here are a couple of audio stories from NPR about phenology.
If you want more information, you might want to pick up The Weather Makers: How Man Is Changing the Climate and What It Means for Life on Earth by Tim Flannery. Flannery does a good job of explaining what evidence scientists are examining and related politics.