I’ve gone through past records and given a summary of the changes that our climate has undergone in the past. I thought it might be fun to go through with a mock summary of what our climate could look like in the future. In the past 100 years Portland has warmed by approximately 1.5ºF. I’ve found that this has had an affect on our climate averages based on a compilation of extreme temperatures and their averages. In the past 60 years Portland Airport has moved from Zone 8a (15ºF) to near zone 8b/9a (20.3ºF).
The past shows us the future
In college when I studied climatology I learned some very important ideas about how you characterize the climate of the past. You actually look at the composition of flora and then reconstruct the climate based on the modern analog of plant distribution. For instance pollen records are found from the anaerobic mud of lakes (there pollen is preserved and does not decompose for thousands of years without oxygen) , carbon dated then re-constructing the flora at the time and comparing it to modern analog plant distribution. You can tell an awful lot about the climate by the native ranges of plants. For example you can summarize our climate from the height of the last Ice Age approximately 10,000 years ago (much colder and drier- likely akin to east of the Cascade Crest at 4000′ ) and then through what is known as the interstadial (a period of warmer weather peaking 6000 years ago) and then to the present. Until the specter of global warming we were actually headed back into an ice age and long term temperatures were on the slide.
The climate is always changing
Studies of past climate perturbations show that there has been a very complex set of influences on climate. Solar activity, ocean currents, CO2 levels and more factors must be combined to get a clear picture. What this means is that some parts of the globe change their climate at different times. It does not all heat and cool like a cup of coffee in a microwave. Things dip and sway, heat and cool and this elegant dance is what drives global climate shifts. Overall, climate change on a global scale requires changes on a global scale. Global warming- greenhouse gasses is as profound a global influence as has ever occurred in the history of humans on our planet. That does not mean that we haven’t endured climate change in recent human history. The Little Ice Age (1350-1910) is one such switch which had a profound effect on humanity. Driven by a low in sunspot activity (The Maunder Minimum) – a lowering of solar insolation (the sun’s heat output) combined with enormous volcanic eruptions which pumped gasses and material to block the sun, this period of much colder weather caused winters in the Northern hemisphere to plunge and glaciers advanced. And all of this was just 1ºC lower than current levels. In Europe the cold had a profound effect. It has been tied to everything from famine to the outbreak of disease. A good way to remember the influence of the Little Ice Age is its depiction in the art and literature of Europe at that time. Ice skating was common on canals in The Netherlands, in England Dickens idealized winters of snow and cold, in fact the very idea of a white Christmas originates from this time.
South Moves North
During the interstadial warm period several things happened that will likely be pertinent to our immediate future. For instance, this warmer period also saw the duration of summer drought expand in Western Oregon. What this means is that it favored drought adapted species. Oak and Ponderosa both expanded their range at the expense of more water loving species. In southern Oregon where there still occurs the hybrid oak the Mohr Oak (Quercus wislezenii x Quercus kellogii) we know that Quercus
wislezenii – California Interior Live Oak- whose range now is exclusively Californian must have occurred in Oregon for that hybrid to be present as it is still. Most likely the Willamette Valley of that period had the climate and plant communities now found 250 miles to the south in the Rogue River Valley. Portland, you were Medford. Hotter and drier for a longer annual period.
Super compressed climate change
Even the Little Ice Age occurred over a period of centuries (with dips that manifested in decades) but the temperature overall fell just 1ºC over that time period. What if you ramped up the change and compressed it into just a few decades? Well, even if you stopped the input of all carbon into the atmosphere tomorrow what we’ve already contributed has set us on an unstoppable path of warming. According to the U.S. Fish and Wildlife warming will continue and actually INCREASE through the rest of this century and beyond. Conservative estimates are that we will rise 2ºF in the 2020’s, 3.2º+F by 2040 and a whopping 5.3º+F by 2080. (Remember we’ve increased just 1.5ºF in the last 100 years.). What effect this will have on native plants has yet to be realistically described as far as I can tell. Species that are in the most finely balanced biomes are likely to fail and plants with greater adaptation to enhanced summer drought and longer growing seasons will likely persevere. Remember that great shifts in climate in the past offered plants plenty of time and un-human obstructed paths to move. But what about our gardens? Increased length of summer drought, longer growing seasons, much higher winter and summer temperatures all will have a profound effect.
A modern analog to Portland’s future climate
I looked carefully at the weather records of cities on the west coast to surmise a future for our gardening climate. Location and climate is influenced just as much by local conditions (topography, latitude, ocean influences) so there will not be an exact analog ever. Instead my study of weather records showed some more general descriptions and I have to say that what I came up with is much more of an educated guess than purely scientific. If as during the interstadial warming period the climate appeared to have shifted north it was my estimate to look to our south for a glimpse at our future. And remember that we are not only at a higher latitude but we are closer to sources of arctic air as well. This also does not take into account annual precipitation which is slated to stay the same or increase. I focused primarily on temperature averages.
Santa Rosa, California- Portland, 2060. Yep. After poring over records and tying them to our projected temperature increase this one location stood out above the rest. You have to know a little about our climate to understand why we will evolve close to this. One is proximity to the ocean and marine influence. Santa Rosa is closer but we have just about the same amount of modifying ocean influence- this holds down both their and our summer time highs. Santa Rosa is also drier than we are (but not by much 32.28″ for them, and 35+” for Portland). So, I compared overall average temperature as well as days above 90ºF as well as days below freezing and Santa Rosa kept popping up on the list. This is based on the rate of increase given by experts. In 2060 our climate will have undergone a striking change and I surmise what we grow in our gardens will have as well.
Portland vs. Santa Rosa
With a projected annual increase in temperature of 4ºF by 2060 there will be stark differences from today and even more stark differences in what we can grow. For instance, Santa Rosa of today experiences 30.2 days below freezing- compared to Portland’s current 44 days. 28.9 days in Santa Rosa rise above 90ºF (Portland’s current average is 14- and remember last year broke the record for the most days-29). Portland’s winter time temperatures will increase dramatically. From an average high in January of 47ºF we could see the mid 50’s. So what will grow here? I anticipate a lot more Palms. Heh. We will be squarely zone 9 by that time. Many more Australian plants as well as possibly even subtropical plants. We will have a much longer period of summer drought. Water use will have to become much more responsible.
Climate Change and our Responsibility
Plants are adaptable but the pressure we are going to place on native plants means that we should be stewards above all else to ensure their survival. Gardeners are adaptable and I have absolutely all the faith that our gardens will be just fine. Most of all we have to pay attention, learn, and adapt with our rapidly changing climate.