The sun provides nearly all of the energy for our climate system. The energy in the Earth's core is small by comparison so it can be neglected in most cases. The impact of volcanic aerosols generated by that internal energy is not negligible. Large volcanic eruptions, especially near the equator, can cause significant cooling for a year or two by reflecting solar energy and by absorbing solar energy higher in the atmosphere where it is more easily radiated to space. These aerosols, primarily sulfur based, change the chemistry of the atmosphere as well. There is a complex interaction of albedo, radiation height, radiation type, radiation intensity and chemical processes that all impact climate. Like we really need more complexity, right? The last three of those variables combine to create the most uncertainty in my mind.
The newly released Cern CLOUD report indicates that cosmic rays that increase in intensity during a solar minimum interact with the trace compounds in the atmosphere to create small particles that can "seed" clouds. These particle provide a surface making it easier form water molecules to condense. The particles created by cosmic ray interaction are smaller than required for efficient seeding of clouds. This process and the size of the particles present a statistical challenge for climate scientists.
Cosmic rays that penetrate the atmosphere increase as the solar energy decreases. If the cosmic rays increase cloud formation, the impact would amplify the change in solar energy which I have shown previously is on the order of 0.18 Watts/m^2. Albedo change provides a much greater change in solar energy absorbed, so more clouds would provide the umpf. By itself though, the change in cosmic rays doesn't appear to be that significant. Volcanic activity can amplify the cosmic ray impact by providing more feed stock for the chemical process. This increases the material and time for the cosmic rays to build bigger seed particles. With the volcanic aerosols more in the high atmosphere near the equator, more water vapor is available to form clouds around these particles.
This leads to a bit of a paradox, in order to trip the Earth system into an ice age, the Earth would have to be warmer than normal for there to be enough water vapor for a rapid change. Climate records show that climate is constantly changing with two set points, warm periods and ice ages. In either of those set point ranges there are minor warm periods and minor ice ages. The minor periods are primarily in the northern hemisphere where the percentage of land area to ocean area is higher. So these minor periods are "regional". With enough of the right conditions, these "regional" events have global impact.
This year's northern hemisphere weather shows how important the northern hemisphere is to global weather. Snowfall and spring precipitation pushed records thanks to the La Nina inspired change in weather patterns. The change is water vapor distribution has the potential to create snow pack deep enough and snow cover wide enough to increase albedo or reflectivity. The extent of the snow cover was not far enough south to have a major albedo impact this time. But imagine if you will, the snow that was in all lower 48 states, being a little heavier and lasting a little longer. The snow cover below latitude 45 has much greater impact on absorbed energy than the snow pack above latitude 50. The closer the snow gets to latitude 30 the much greater the impact becomes. So did we dodge a bullet? Maybe.
While the past year had a good amount of volcanic activity, most was above latitude 45 north or below the equator. This is not to imply that the volcano has to be located between the equator and latitude 45, but the aerosol cloud from the volcano impact the area between the equator and latitude 45 with the right mix of chemical compounds. The Laki volcano is located in Iceland near the arctic circle. When it erupted in 1783, it produced strong cooling dropping the average winter temperature in the US by nearly 5 degrees C. Thirty years later, Mount Tambora in Indonesia erupted causing a colder spring and summer. The location, timing and concentration of volcanic eruption greatly impact climate.
So how can these factors combine into the perfect storm? A large volcanic eruption with the impact of a Laki in the early spring, during a prolonged solar minimum during early transition to a cooling Pacific Decadal Oscillation with a strong La Nina could produce an increase in albedo of up to 5 percent in a very short period of time. If the volcanic climate cooling persists for two years approximately, we could tip into an ice age, minor or possibly major.
While I still have some work to do, somewhat surprisingly it looks like increased CO2 may provide enough water vapor increase to drive the cooling deeper than other wise. I will leave this with a link to a NASA animation of water vapor changes in 2005. If I can dig up the information for 2010 - 2011, the comparison may be interesting.
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