Mankind Is the Main Cause of Global Warming

1500-Year CyclesThe 1500-year cycles are not global. Most of the data that scientists have found on this has come from the northern hemisphere. However, in the southern hemisphere, the exact opposite trend happens. In other words, whenever the northern hemisphere is warming, the southern hemisphere is cooling, and vice versa. "Whereas Antarctic and Greenland climate records do exhibit approximate anti-phase behavior around 50% of the time, they are generally in phase during cooling. A phase lead of Southern Hemisphere climate of 1000-1600 years is statistically indistinguishable from a lag of 400-800 years, whether for Dansgaard-Oeschger [1500-year cycles], Heinrich, or longer-duration events. The "seesaw" or "Southern lead" appearance of the data arises from the fundamentally different characeristics of the climate series, most importantly the absence of rapid warming events in Antarctica comparable to those in Greenland". [1]However, in the current case, we see that both the northern and southern hemispheres are warming, meaning that it cannot be due to the 1500-year cycles. [2]Human Emissions of Carbon DioxideThe claim that CO2 levels were higher during certain ice ages is based off of old, faulty data. A recent study found that the levels during the Ordovician era (the era most climate skeptics focus on when making arguments like this) were eight times below pre-Industrial levels. This is indeed still a little high, but it's also important bearing in mind that the sun was dimmer then. During the Ordovician era, the sun was 4% dimmer. This meant that higher CO2 levels would have been necessary for Earth to have not been frozen over. This is based on established nuclear models of main sequence stars. Considering all of this, ". .. over the long term, there is indeed a correlation between CO2 and paleotemperature". [3][4][5]Apparent Mismatch Between CO2 and Temperature IncreasesIt is true that the vast majority of the warming happened over the 20th century. However, it is also true that the vast majority of the CO2 emitted into the atmosphere was emitted over the 20th century. See the graph below[6]: It is easy to see that only a small fraction of the emitted CO2 was emitted before 1900, and this correlates with the fact that only a small fraction of the temperature increases occurred before 1900. Amount of CO2 EmissionsAny CO2 emitted into the atmosphere would have an adverse effect on the climate. As I said in the last round, there was a study that said, using a Bayesian statistical approach, the climate sensitivity as maximum 4 degrees C, a mean of 3 degrees C, and likely value of not lower than 3 degrees. This means that the CO2 that humans emit thus has an effect of 3 degrees C per doubling of CO2. This can be shown by the fact that CO2 concentrations have increased from around 275 ppm to around 400 ppm. This is an increase of around 40%. This should manifest itself with a temperature increase of a little less than 1.5 degrees C. This is indeed around the amount of global warming we have seen so far. It should not be more than this. [7][8]If less CO2 had been added into the atmosphere, then the planet would have warmed less, but it still would have warmed. This would be true for any non-zero amount of CO2 emission. Climate ModelsThis point is irrelevant. The climate is much more complicated than just a correlation between CO2 and temperature (even though it still exists). Climate models have to be extraordinarily complicated, and even so, they might leave out very important climate forcings. Even if they didn't, there might still be glitches in the models that would make the model give an invalid result. The ability for climate models to accurately predict the climate is completely independent of the whether or not CO2 levels are related to temperature levelsIt is worth falsifying the notion, however, that there has been no warming since 2000. This idea is based on satellite measurements of atmospheric temperature. However, there are two problems with this. One, while the atmosphere accounts for only less than 3% of increased heat content, the oceans account for the vast majority, and they show no such trend. [9] The graph below shows this[10]: And two, there have been a lot of negative short term forcings over the last 20 years. Removing the short term trends of the extremely powerful El Nino in 1998, volcanic activity, and solar activity, the atmospheric temperature plot looks more smooth[11]: (You can faintly see what the plot looked like before the negative forcings were removed; the variability after 1998 makes any analysis before a statistical reanalysis suspect). Correlation Between CO2 Emissions and CO2 LevelsMany studies have shown that the "airborne fraction", or the fraction of human CO2 emissions that stay in the atmopshere, is around 43%. The fact that the CO2 levels flatlined during WWII is actually rather complicated. While military activity spiked, other industrial activity plummeted and millions of people died, decreasing the need for non-military CO2 emission even lower. In addition, CO2 levels are not known with the precision necessary to unravel this mystery before 1960, due to improper measuring techniques. There are simply too many factors too consider to make a sound conclusion here. As for the apparent 800-year lag in CO2 levels after temperature increases, this is indeed true. However, this is because there was no non-natural (i. e. human) forcing of CO2. Instead, another forcing initiates the warming trend, and CO2 amplifies it. "When the Earth comes out of an ice age, the warming is not initiated by CO2 but by changes in the Earth's orbit. The warming causes the oceans to release CO2. The CO2 amplifies the warming and mixes through the atmosphere, spreading warming throughout the planet. So CO2 causes warming and rising temperature causes CO2 rise. Overall, about 90% of the global warming occurs after the CO2 increase. "[12]Human Versus Natural CO2 EmissionNatural CO2 emissions are typically stable, meaning that there is rarely any long term climate change that results from natural emissions of CO2. However, humans have emitted a lot of CO2, above and beyond what is naturally emitted, and this unbalances the climate stability. "Although our output of 29 gigatons of CO2 is tiny compared to the 750 gigatons moving through the carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra CO2. About 40% of this additional CO2 is absorbed. The rest remains in the atmosphere. "[13]Solar ActivityThe most important of the natural climate forcings is indeed the sun. It is the source of the Earth's energy. This energy comes from the radiation emitted as a result of fusion reactions at the core of the sun. This radiation is known as the Total Solar Irradiance (TSI). Any change in the TSI causes energy imbalances on the Earth. This energy imbalance can be calculated using the formula below[14]: Delta means change, so Delta(F) means the change in energy (i. e. energy imbalance) and Delta(TSI) means the change in solar irradiance. The 0.7 factor comes from the fact that the Earth reflects about 30% of the solar radiation it receives, and the 1/4 factor comes from spherical geometry. Changes in temperature are proportional to the energy imbalance. This can be expressed in the formula below[14]: Lambda is the constant of proportionality, representing the climate sensitivity (discussed in my first argument) in this case. The only thing that's left is to actually determine the values. First, the change in TSI (in this case, between 1900 and 1950). ". .. we'll estimate the change in TSI at 0.5 to 2 W-m-2. " This corresponds to an energy imbalance of around 0.1-0.35 W-m-2. Next, the lambda factor. I explained in the last article that the statistically most probable value for the climate sensitivity was around 3 degrees C. But, there was a lot of variation. "Studies have given a possible range of values of 2 to 4.5°C warming for a doubling of CO2, which corresponds to a range of 0.54 to 1.2°C/(W-m-2) for λ. " This gives range of values from 0.05 to 0.4 degrees C, with a most probable value of 0.15 degrees C (corresponding to the statistically most likely climate sensitivity). In other words, solar activity from 1900 to 1950 raised the temperature of the Earth 0.15 degrees C. Looking at the effect of CO2 emissions over that same period, humans increased the concentration of CO2 in the atmosphere by about 20 parts per million, giving a range of values of 0.14-0.32 degrees C for the effect of that emission on the climate, with the most probable being 0.22 degrees C. [14][15]This corresponds to CO2 amounting for 60% of the warming from 1900-1950. After that, it gets higher. CO2 emissions rise exponentally, and changes in the TSI start getting less positive, and eventually become negative after 1975. "Over the past century, this increase in TSI is responsible for about 15-20% of global warming. But since TSI hasn't increased in at least the past 32 years (and more like 60 years, based on reconstructions), the Sun is not directly responsible for the warming over that period. " Solar activity cannot account for the warming after 1975, and even before that was a smaller factor than CO2. [14][15]This can be shown in the image below[16]: Therefore, we see CO2 correlates with recent temperature increases better than solar activity, especially after 1975. Long Term Forcings and MarsThe cycle of radiation is so long that it would not be having the sudden, enormous effect we've seen over the last 150 years. As for Mars, the studies concluded that it was a change in the surface dust, not solar activity, that caused the warming. Surface dust has a massive effect on Mars's climate. The supposed warming trend went from before the surface dust change to after it. Therefore, Mars did not warm because of solar activity. [17][18]SourcesSources in comments.