Ten Causes of Warming: The Layperson’s Checklist

I appreciate your inability to help me, so please allow me to try and help you.
I do not dispute the data or the conclusion regarding the central valley in CA.
I am trying to be very emphatic about that.
It is the generalization from that result to a broader conclusion about the effect of vegetation in other climactic and ecological circumstances where you are going astray.
Water is the great moderator of the surface and the atmosphere.
Adding water to the air where it is extremely dry will not have the same effect as adding the same amount where there is already plenty of moisture in the air and in the ground.
Likewise, vegetating a desert will not have a simple inverse effect as chopping down a forest.
Forests generally exist where there is at least a certain amount of water, typically that for at least some of the year, there is more rainfall than can evaporate and/or transpire. In physically geography, which is one of the areas I have studied intensively, this referred to as a place where precipitation exceeds potential evapotranspiration (PET). The equivalence line for this relationship is broadly defined as the transition line from humid to arid climate and zones.
Of course, there are areas where it is humid for part of the year and arid for another part.
Deserts are places that are arid in every month of the year, climatologically speaking.
These are definitions, and are based on what is actually seen and measured.

Because climates vary from place to place, making a similar sort of land use change in one area may have a drastically different effect than the same change in another area with a different climate regime.
Additionally, making a change in one small area, like clearcutting a patch in a forest or irrigating a small island in the middle of a desert, may and likely does have a different effect than making the same change over a far wider area.
And as well, the short term effect may not be the same as the medium and longer term results.
Having an oasis spring up in the Sahara desert will not cause more rain in the desert, but irrigating the whole desert and planting trees over it all certainly would.
Once established by a rainy climactic period, a forest in what once was a desert region can become self sustaining to at least some degree, even after the amount of rain begins to decline again.
Periodically burning zones that were once forested and are transition zones between humid to arid climates has produced savannahs in various large regions of the world. A savannah being a place where the tree cover does not form a closed canopy and sunlight can reach the ground, allowing for an understory of flora, typically but not necessarily grasses.

The moderating effect of water on the climate regimes of a particular place means that where water makes one place cooler, the same body of water or amount of rainfall will make another place warmer. This moderating effect may be mostly in one part of the diurnal cycle, or the whole of it. It might cool daytime and warm nighttime. It may produce a different change in one season than in another. In fact, we can find places in the world where each of these things is true, measurably and verifiably.
Finding specific examples is easy.
But one must be open to the full range of factors that influence the Earth, and the full diversity of landforms and climate zones.
Overgeneralizing will often lead one from a valid observation to an incorrect conclusion, and not only regarding matters of climate related issues.
Complicated things cannot be described by simplistic generalizations…not if one is interested in being correct in a broad sense.
One such oversimplification and the result of too many people accepting that one factor is so predictable and controlling in it’s effect is exactly why we have the CAGW imbroglio, which threatens our very ability to maintain an industrial society.
Getting it wrong a different way will not help.
I also have a chemistry degree, but I studied the whole range of scientific disciplines during by time at a university, and also did so long before I got there and long after I left.
I have done all sorts of different things in my life, and many of them involved being outside all day, and many times all night as well, in all sorts of different places and making all sorts of real world observations.
It is very easy to understand that the world is a big place with all sorts of things going on, all sorts of wildly different conditions that change from place to place and time to time in all sorts of ways, some common and some quite unusual.
I took an interdisciplinary approach to life and to my education and to the work I have done because I recognized that, although we subdivide the world and sciences and fields of discipline in all sort of ways in various categories, these are not analogous to the natural world, where everything is happening at once and all factors interact in many ways.
Some who knows everything there is to know about physics, but nothing else, or a person who knows everything about the flora and fauna of the planet, but nothing else, will both have different ideas about how they think the Earth behaves, but neither will ever likely be correct.
Because there is no way to understand a complex system by focusing on and giving too much weight to one factor, while ignoring other ones.

The moderating effects of water and water vapor are a critical part of understanding our planet and the living things that inhabit our planet.
Water in any of it’s three phases can and does cool, and can and does warm, depending on where and when and in what amount the ice, snow, water vapor, clouds, rain, lake, ocean, or river exist.

Snow across a wide extent of the US early in the winter, that persists for an extended period of time, will have the effect of making areas that are snow covered, as well as adjacent areas, colder for the whole season. But snow in one particular place, as opposed to no snow cover, will insulate the ground and lessen the depth to which the ground will freeze in Winter.
A bout of heavy rain in the middle of Winter can melt a huge extent of snow cover, and cause the nights to become less cold, but also the ground to become colder and freeze deeper than if the rain had not melted the snow.

Having an ocean nearby makes nearly anyplace, but not everyplace, on Earth be generally cooler by day in Summer, but warmer by day in Winter. But not if it freezes over.
Being near an ocean moderates temperatures, tending to make them less extreme than areas just inland. Right along the coastline the effect is strongest.
Being next to an ocean makes San Francisco far cooler than the areas a few tens of miles inland, but here in Florida, being on the south side of a lake will prevent many winter frosts and freezes and be the difference between a rich citrus farmer and the bankrupt one who bought and planted a mile north of the lake.
Philadelphia and Southern New Jersey get a small fraction of the snow than areas just a few more miles inland get. Part of the difference is due to elevation, but a large part of it is due to the marine influence.

Similar examples can be given for places that have a different climate regime due to the difference in humidity levels of the air, which directly effects what the temperature regime will be and what the dominant vegetation is.
So whatever one can say, and that is true, about the effect of irrigating and planting crops in the central valley of CA, becomes false when extrapolated to infer a general rule which is valid for the planet as a whole.
It is an extreme place, and the main reason why is the widely varying and typically insufficient amounts of moisture available, so adding more on a continuous and ongoing basis makes the place less extreme.
Irrigating a place in Illinois which is having a once in five or ten years drought will not have the same effect on the long term average temperature of the region.
Cutting down a forest in the Cascadia region of Washington state will not make it cooler due to the removal of “heat trapping” coverage by tall trees. It will get hotter at the level that temp is measured on every day that is sunny. Forests, plants in general, gather solar energy and transpire water. Tall trees also block outgoing IR from the ground by dint of the foliage cover.
So the ground level in a forest is shaded by day and thus cooler. The air above the forest is cooled by transpiration from the unbroken canopy of trees. Removing the trees will make it hotter in the day and probably cooler at night. The relative amount of each effect will vary depending on the length of the day vs night, cloud cover (on a cloudy day or night, it will be less different below the canopy than above it compared to sunny days or nights), and how much rain has fallen…how wet everything is.

Here in Florida, under a native live oak tree the daytimes are cooler by many degrees.
But the nights are warmer than a place two feet outside of the canopy of the trees. The effect is strong enough to make it easy to grow certain tropical plants under the oak trees in dappled sun, but impossible for them to survive year to year only a few feet away.
I have had entire crops lots, utterly destroyed, to frost in a single period of a few hours on one night of the year, and at the same time had a bunch of the same plants completely undamaged that were right next to them but under the canopy of a single oak tree. That was due to the inability of frost to form where radiative cooling is blocked, but the temp is above freezing (frost forms at 38°F under clear sky with no wind). A row of Ficus benjamina planted as a hedge was killed in a hard freeze (frost will cause defoliation by not kill wood on this species), right down to ground level, the same night as the space shuttle crashed due to the cold (our nursery was 17°F that night, measured out in the open, and is located 103 three miles nearly due West of the Cape)but the sections of the row beneath an oak tree were undamaged.

Consider this: What happens to the CA central valley if all irrigation were to cease, vs what will happen to the clear cut area in Cascadia, if the prevailing conditions are left to do what they will.
That desert will quickly become a desert again, because the row crops and nut and fruit trees will quickly dry up and die. The temperature regime will return to whatever it was prior to the interventions of people. Only the moisture is keeping it the way it is.
In Cascadia, the trees will grow back, faster or more gradually depending on several factors, it within a few decades it will be rapidly returning to exactly as it was. The climate will not have changed. Cascadia will remain a moist and mostly coolish place, and the San Joaquin valley will remain a desert. Just look how fast farmers lost trees that were decades old when their water allocations were cut.

In more marginal places, making drastic changes to the local flora can have longstanding results however, as when forested areas were converted to savannah by periodic burning by people, or when adding one one-hundredth of one percent more of CO2 is causing vast cumulative areas to spontaneously increase aerial plant coverage all over the world, including places like the Sahel zone in Africa.
And much of the rain that falls on continental areas comes from water vapor that was transpired by trees on the continent and often in that same area, so adding or removing large areas of vegetation can have wider and longer term climate effects. This same fact is why drought often begets more drought. Although since nearly every drought ends in a flood (it takes a flood to erase a long term drought), obviously other factors eventually overwhelm this local one.