Still don’t believe in climate change? Take a look at tree ring data
NASA scientists use tree ring data to measure draughts and build statistical models that predict how climate change will affect our planet
The weather is fickle — so much so that climate change skeptics usually argue that global warming is a false phenomenon since the Earth’s weather has always fluctuated between hot and cool periods. Moreover, as these skeptics typically go on to say, how do we know what the weather was like a thousand years ago anyway? We have no temperature records, precipitation data, or climate information from the past to prove that what we’re experiencing in our century is drastically different from what the planet has experienced before.
Fortunately, we actually do have precipitation data about the past — and it’s hidden right in our backyards: trees.
As Benjamin Cook from the NASA Goddard Institute for Space Studies explained at a recent Moore Sloan Research Lunch Seminar, scientists sometimes use trees to gather data about climatic conditions about the past because of the unique way that they grow.
Trees take approximately one year to grow a new layer of wood, and each new layer is called a tree ring. Not only do the number of rings reveal how old a tree is but, interestingly, the amount of space between each tree ring (i.e. how thick each new layer of wood is) reflects how much moisture the tree received that year. For example, enough moisture and a strong growing period often results in a wide tree ring, but a dry drought season will mean a narrower ring.
The climate conditions of the past are recorded in the wood — meaning that we have evidence about past climates that stretch as far back as 800CE. And, what the tree ring data confirms — along with satellite image data about our planet’s changing geography and global temperature records — is that our plant is, indeed, warming up at a distressing rate.
And, not only are scientists using tree ring data to confirm that global warming exists, but they are also using the data to predict how our climate will change.
“Obviously,” Cook said, “we don’t have data from the future. But we can use climate models to investigate future climate changes for different emissions scenarios.”
Cook went on to describe how he, his research team, and other scientists around the world are using our existing data to create models that predict how our planet’s climate will change depending on the different courses of action that we take as a global community.
Examples of these scenarios (or, as scientists say, Representative Concentration Pathways) include speculating about what would happen to our planet if we mitigated our greenhouse gas emissions, compared to what would happen if we took no action at all.
This predictive work requires an extraordinary amount of computing power and resources since each scenario needs its own model — which is why this has become a collaborative effort across multiple climate network temperature stations around the world.
So far, preliminary results from their multi-modal ensemble based on tree ring data and climate models predict that the future in water stressed regions like western North America will become even dryer than the extended dry spells of past centuries. “If we continue warming at the current pace,” Cook warned, “a megadrought by the end of the twenty-first century is virtually certain.”
by Cherrie Kwok
What does this graph mean?
Top: Multimodel mean summer (JJA) Palmer Drought Severity Index (PDSI) and standardized soil moisture at 30 cm (SM-30cm) and 2–3 meter depths (SM-2m) over North America for 2050– 2099 from 17 climate model projections using the RCP 8.5 (high warming) emissions scenario. Dashed boxes represent the regions of in- terest: the Central Plains (105°W–92°W, 32°N–46°N) and the Southwest (125°W–105°W, 32°N–41°N).
Bottom: Regional average time series of the summer season moisture balance metrics from the tree ring reconstructions (brown line) and climate models. The tree-ring based drought index is smoothed using a 50-year loess spline to emphasize the low-frequency variability in the paleoclimate record. Model time series (PDSI, SM-30cm, and SM-2m) are the multimodel means averaged across the 17 CMIP5 models, and the gray shaded area is the multi- model interquartile range for model PDSI.
