Changing Climate

What is climate?  You may have heard that a super warm summer or a super cold winter is NOT climate change.  This is certainly true.  A whole string of such events, or a distinctive pattern of warming or cooling seasons is different.
Climate refers to long term trends in not just temperature but also rainfall, wind patterns, humidity, cloud formation, etc.
Climate can be global or local.
The other rather indisputable fact about climate is that earth has experienced more or less constant change in climate, with warming and cooling trends over the millennia of existence.

The real issue with all the news-buzz over “global warming” is not whether or not it has been occurring (on that we know the answer is yes) but more about what role human beings (e.g. fossil fuel emissions) have played, and what responsibility we might have to the planet and other life.  It is becoming less and less debatable that anthropogenic (human derived) green house gas emissions have played a role in global warming;  it’s hard to dispute the current rise in global temperatures and the accompanying increase in CO2 (nearly doubling in atmospheric concentration) since the industrial revolution.
A couple of key questions still to be answered include:

• Are humans the only factor causing global warming?
• If humans have indeed played a role in global warming, what is our responsibility to moderate or mitigate these effects?  (Should we care?)

The second of these seems like an issue of ethics, but it is worth noting that human beings are not the first life forms on earth to have wrought havoc with atmospheric and oceanic composition, and with climate.  Around one billion years ago, the rise of photosynthetic cyanobacteria, and with the filling of oceanic oxygen sinks, atmospheric O2 concentrations rose dramatically.  For many creatures at that time, this was a poison gas, and it additionally modified the warming effects of CO2!
Of course, there’s a big difference.  Cyanobacteria don’t have much in the way of conscience; hopefully most humans do!

https://en.wikipedia.org/wiki/Geological_history_of_oxygen

Above,  O2 through time (Ga= billions of year)
The idea here is not that oxygen affects climate, but simply that major atmospheric changes have occurred in the past.

Climate Change Time Scales

Relatively recently, within a century (or two or three), winters were much colder in the northern hemisphere.
The canals in Holland used to freeze over quite regularly, providing a delightful and picturesque avenue for skaters.
See the painting below, by Dutch master Beerstraten

The Village of Nieukoop in Winter, by Beerstraten, c. 1650
This time period (and Beerstraten’s painting) would fit with what was referred to as the Little Ice Age.

The climatic shift from the Medieval Warm Period to the Little Ice Age may well have been one of the primary factors that led to the demise of Viking colonies in Greenland and the northeast coast of America.  Without this climate shift, would the U.S. have more of a Nordic heritage?  Who knows…

J. Sauer, USGS,, Temp Proxy for last Two Millenia

But what about going deeper into earth’s past?  What about pre-recorded time, i.e. geological time?  A key tool for deciphering past climate is the oxygen isotope “proxy.”  This is based on fractionation of O-18 (oxygen with 8 protons and 10 neutrons) and O-16 (oxygen with 8 protons and 8 neutrons), which are both naturally occurring.
Fractionation refers to how this ratio is modified by natural processes, notable evaporation.
The key idea is relatively simple– during cold periods O-16 is preferentially removed from ocean water (as water containing O16 is lighter and easier to evaporate than O18-water), but is then trapped in snow and ice and does NOT return to the oceans;  so during cold periods, ocean water becomes O18 enriched.
Review these videos for more info on the O-isotope proxy

from Penn State,  (See “Stable Isotopes, Videos 1,2,3)
https://www.e-education.psu.edu/earth103/node/5

Using this sort of technique, and the analysis of both ice cores (Greenland and Antarctica) AND sea-floor sediments, we can go vastly further back in our evaluation of past climate.
Here is a plot showing temperature variation over the last several hundred thousand years, a key time period in human evolution.

and, below is a plot showing temperatures back to the beginning of the Cenozoic Era (“age of mammals” that began around 65my, at dinosaur extinction time).

both plots, after Rutledge 2013,,http://www.alpineanalytics.com/climate/DeepTime.html

A really deep time look at temperature fluctuations!

From the above plots, it’s clear that earth history is indeed one of cycling climate and global temperature.
Especially looking at the plot for temperature over last several hundred thousand years, we see evidence for some sort of pulse or periodicity.
Indeed there is good reason to see this pulsing of warm and cold, over tens of thousands to hundreds of thousands of years– a product of earth’s changing rotational and orbital features!
We owe the initial recognition of this “astronomical” forcing on climate to a relatively little known but talented polymath scientist of Serbian descent, Milutin Milankovitch, who lived in the late 1800’s and early 1900’s.
He was the first to suggest that well known and periodic shifts in earth orbit and spin characteristics could significantly affect incoming solar radiation and thereby generate climate pulsing.
On a 100ky cycle, earth’s eccentricity changes back and forth.
On a 40ky cycle, earth’s tilt wobbles a bit, back and forth.
And, On a 20ky cycle, earth’s rotation axis describes a small circle, much like spinning toy top.  See below

Below is a video tutorial on Milankovitch Cycles.

https://www.sciencecourseware.org/eec/GlobalWarming/Tutorials/Milankovitch/

What does the future hold?

The climate system is not simple.
It’s not just about our atmosphere, but also ocean circulation, volcanism, continental changes and albedo (reflectivity).  And, as we just saw, it’s also about external forces associated with planetary orbit and spin, and perhaps also with variations in solar output.
Keep in mind, this complexity doesn’t suggest that science is useless with understanding past and future climate.  Quite the opposite.
We’ve come a long way in understanding earth’s climate system, we’re becoming aware of human contributions to climate change, and it is certainly now time to bridge the gap from science to societal action!