An Intuitive View of the Climate System - And a Surprising Result
Viewing data graphs as pictures in an exhibition
Where do science and art overlap? Is there something that they share?
This essay began with the creation of a number of graphs charting major indicators of our changing climate system. Recognizing patterns and similarities in those figures brought to mind the intuitive, visual way we might encounter paintings in a gallery.
Perhaps content and color and pattern create your first impression, rather than technique or materials.
Can visual presentations of climate data be viewed in the same way – by concentrating on the form and outline rather than the specific numbers or the details of how the graphs were created?
Think of this as a way to avoid being distracted by all those tiny, descriptive placards on the wall in every gallery!
So this essay builds on a series of graphs that capture the major trends in the climate system since 1970, along with trends in population and economic activity that drive those changes, all set in a graphical context.
As you wander through these graphs, I hope you might notice first the emergent patterns in each, as you might with a painting, and then note the consistency of those patterns across images.
(Note: All those necessary details on sources and units, as on those placards on the wall in the gallery, are provided in an accompanying essay – we do need to show that the numbers in these graphs are real!).
OK? Let’s give this a try.
The context – a map for this tour of our curated data sets.
There are three major themes to the tour that the following images will try to convey:
1. The different parts of this system are very tightly linked. You can predict change in one from changes in others.
2. They are all moving in the same direction, driven by human actions.
3. We can change the path we are on, but it won’t be easy.
Are the parts tightly linked and moving in the same direction?
Our first two images capture the impact of human activity represented in the top box.
The image on the left shows the ever-upward trends in population, economic activity and greenhouse gas emissions driving climate change. However, the image on the right says that the rate of population growth is decreasing, and that while per capita income is rising, the global economy is becoming more carbon efficient (lower emission of carbon dioxide per dollar of GDP – gross domestic product). All good things!
But at the same time, accumulating emissions are driving a very steady increase in the carbon dioxide concentration in the atmosphere, which is driving the measured increase in global temperature, which in turn is driving increased storage of heat in the oceans.
So human actions and the top four processes in the climate box are all very closely related. There are good scientific reasons why they should be, but the first time I graphed all of these simultaneously, the degree of agreement was astonishing.
Are the patterns in these images clear and do they communicate where we are with climate change?
Here are a few more. Global temperature increases affect us all directly, but also indirectly through subsequent changes in the climate system.
Changes in late-summer ice coverage in the Arctic Ocean is one of the most visible effects of global warming, and the continuing loss of melting ice from the Greenland ice sheet (as an indicator of loss of land-based ice) is a major contributor to sea level rise.
Both sea level rise and an increase in tropical storm activity threaten all coastal and near-coastal communities. Both have been increasing over the last 50 years, and both can be related to ocean heat content (or cumulative emissions, or carbon dioxide in the atmosphere – all of which are closely related!).
It is worth emphasizing again how extraordinary it is that all of these measurements, taken by different groups using very different methods, show such strong relationships.
The take home message from this first part of our graphical tour, then, is that all of the drivers and responses in the climate system are very tightly coupled and have been changing at a relatively constant rate over the last 50 years.
Science says these relationships should be strong, these long-term data sets show that they are.
Where are we headed and can we change direction?
The most straightforward way to answer the first question is just to project the trends over the last 50 years into the future. Relationships in the blue box won’t change, they reflect the basic physics of the climate system.
If we project current rates of change in population growth, per capita income, and carbon efficiency of the economy out to 2075 (and the next essay will provide details on how this is done), we get the surprising result mentioned in the title. Global warming will eventually plateau - and at a lower level than I would have expected.
If increases in the carbon efficiency of the economy really do continue as they have over the last 50 years, then we reach carbon neutrality in 2075, and all the response indicators stabilize. While this is encouraging, temperatures in 2075 would still be more than 1.8 degrees Celsius (3.2oF) warmer than in 1970, tropical storms might increase from 30 to 50 per year and sea levels would be at least 355mm (14.5 inches) higher (and probably much higher – see caveat on predicted sea levels in that next essay).
It’s not a pretty picture, but given 50 years to prepare, perhaps the worst consequences could be mitigated – once we acknowledge that this is happening.
The second question asks if we can change direction. We can. The most sensitive variable here is the carbon efficiency of the economy. If we can accelerate the rate of increase in efficiency such that carbon neutrality occurs in 2050, then global temperature increase would plateau at less than 1.4 degrees Celsius.
If, on the other hand, efficiency gains slow to half the current rate, neutrality does not occur by 2075. Temperature increase would reach 2.4oC (4.3oF) degrees and still be rising, and there might be 60 tropical storms per year.
While easy to say, actually increasing the carbon efficiency of the global economy to achieve neutrality by 2050 or 2075, although a stated goal of nearly every major study and political jurisdiction, will be a huge task.
We can change direction, but it won’t be easy.
Three Images That Bring It All Together
The graphs above represent a very different approach to climate projections than those produced by the complex physical climate models used by the Intergovernmental Panel on Climate Change (IPCC). Is there any common ground between the two approaches?
Let’s conclude this essay and graphical tour with two strikingly simple images that make this comparison, and another icon of the climate change era.
Thirty years of intensive work by scientists and policy makers through the IPCC process has been distilled down to this one relationship (on the left). Think of this as a single piece of art that captures a style or an era for you.
It comes with this banner headline:
Every ton of CO2 emissions adds to global warming
So all the complex climate models and scenarios produced by the IPCC come down to a single, linear relationship between cumulative carbon dioxide emissions and changes in global average temperature. Does our intuitive graphic approach yield the same kind of relationship? It does (image on the right above). Even the absolute values are similar.
As you exit this exhibition, there is a final, classic image by the door that, paired with the IPCC figure above, captures our situation as two iconic paintings might capture an artistic movement. This additional image is the Keeling Curve of carbon dioxide concentration in the atmosphere as measured on a mountain top in Hawaii. Concentrations now are higher than at any time in the last 2-3 million years and continue to increase.
Unless we can bend this curve by lowering emissions, we will continue to ride up the straight line in the IPCC diagram into a warmer and more challenging future.
I hope this approach helps us think of the climate system in an intuitive way as a tightly integrated system and helps us understand where we are going and why.
We can reshape our climate future by reducing greenhouse gas emissions now while also preparing for the changes that are already certain to happen.
Postscript
But wait – what are those processes in the red box at the bottom of the conceptual diagram? They are potentially important feedbacks in the climate system that could shatter the nice clear story presented here. To learn more about these, and the caveat on predictions of sea level rise, you will have to read the other essay!
Sources
All data sources and the units in which values are expressed are presented in the accompanying essay.
The IPCC diagram can be found here:
https://www.ipcc.ch/report/ar5/wg1/summary-for-policymakers/figspm-10/
Data for the Keeling Curve can be found here:
https://keelingcurve.ucsd.edu/
Note: I’ve used the idea of a museum tour before as an analogy for presentation of the science of weather and climate. A much deeper look at both the history and science of weather and climate can be found here:
https://yalebooks.yale.edu/book/9780300259438/less-heat-more-light/