okay so for the second installment of the climate change lecture um we're going to talk now about is human activity a major cause of the warming this is what the ipcc has been asking since their first report in 1990 and in the very first report they answered this question yes and every report that's been done since then the latest one was put out in 2016 i believe the ar-5 there's just been more and more evidence that human activity is the major factor that's causing the warming so let's take a look at this table here because this has a lot of information in it um that helps to support the understanding that human activity is a major cause of the warming so on the x-axis you can see that the measure is what's called radiative forcing relative to 1750 and that represents warming in the atmosphere okay so anything that is to the right of the zero is causing warming and anything to the left of the zero causes cooling so if you look up at the top of the graph here the major bars here that are causing warming because they're to the right of the zero r greenhouse gas emissions these are all the greenhouse gases here the major one being co2 of course so that shows that co2 is the number one main contributor to warming um here's some other gases here like carbon monoxide nitrogen oxides they're also contributing to warming this one's contributing to cooling a little bit um and then we have some things down here that actually contribute to cooling like clouds like particulate matter in the atmosphere and then here we have natural things that contribute to warming which is solar irradiance solar irradiance is the energy coming from the sun and that changes over time and it actually changes according to known cycles that we can model and we can measure called milkanovich cycles and obviously when there's more energy coming from the sun it makes things warmer so nobody is disputing that but you can see from this that contributions from that factor the change in energy coming from the sun is very very small compared to the changes to climate that occur due to greenhouse gas emissions so if we look down here at this bottom part of the graph the term anthropogenic means caused by humans and you can see that the warming is caused by humans um the other thing you can see from this is that the contribution to warming from humans has increased greatly since the 1950s i mean even in the 1950s the contribution from anthropogenic sources was great but now in 2011 it's even greater so we are continuing to contribute more and more to warming as time goes on here's a little bit more about solar irradiance because this is one of the things that climate deniers tend to grasp onto you can still find kind of misinformation on the internet about this people saying oh the climate naturally changes over time everybody knows that and that's why we're seeing warming now we're just in a warming cycle well yes we have been measuring solar irradiance for a long time and you can see of course in this graph the red line represents changes in energy from the sun that's solar irradiance and you can see the blue line represents temperature and obviously these two data sets are related if there's more energy hitting earth from the sun it's going to be warmer so there is a relationship between those two data sets but as you can see from the mid 70s on there there's actually no correlation between these data sets in other words we've seen a lot of warming happen but the the cycle for solar irradiance is on a downward trend so this in and of itself disproves the impact of solar irradiance on climate change it's not a major factor that can explain the incredible warming that we've seen in the past few decades so another thing that scientists have done to really really underscore and prove that human activity is a major factor in climate change is um we compare what they've done in these graphs is compare actual measured temperature increases with measuring the contribution from natural forcings only versus the contributions to increased temperature from human cause sources so that's what these graphs show in these graphs the black line represents actual measured temperature that's what we have directly measured that's what we've actually observed and seen the purple kind of line here or region here represents the contribution to temperature from if you just look at natural forcings if we just look at the natural factors that that contribute to temperature that's what it models out to be so in other words we can't explain what we've actually seen just looking at natural forcings the light pink region here represents modeled temperature change if we include both the natural factors and human activity like increased greenhouse gases in the atmosphere and if we include both those things both of those factors that contribute to climate change the natural things as well as the human cause things look what happens now we're correlating with what we actually measure and we whether we do that on the land whether we do it in the land in the oceans whether we do it in terms of ocean heat we cannot recreate what we've actually observed in terms of temperature change unless we include the human cause factors looking at natural forcings only does not explain what we actually have seen and measured um so this is what we've needed to prove there's a few different things we needed to prove to show that human activity is the main factor we needed to prove that there's a correlation between greenhouse gases that are released by humans and temperature change and we saw that with ice core data that really close correlation between co2 levels and temperature levels in other words there's a root you know if you have increased co2 that really increases temperature but the other thing we've had to show is that there's been increases in these greenhouse gases that they've all actually increased in recent years when humans have been around and that's what we see going back 800 000 years these levels whether you look at co2 whether you look at methane whether you look at nitrous dioxide all these are released by humans and they've all increased in the same way in the last few decades so here again is showing that um the all of these greenhouse gases have been increasing in the same trend as temperature has well how do we know that that has to do with humans besides the fact that humans release this stuff well you could see from these graphs when did the concentrations of carbon dioxide the concentrations of nitrous oxide the concentrations of methane the concentrations of sulfates when did they all start really increasing dramatically look at the dates right around the 1800s well what's the relationship between that and humans that's when we started burning fossil fuels at a great rate and all of these gases are released due to fossil fuel burning so this is a very strong data set that shows that mainly the burning of fossil fuels is contributing these greenhouse gases to the atmosphere so what we have is we have correlation between greenhouse gas gases in the atmosphere and temperature we have data showing that greenhouse gases in the atmosphere have increased dramatically in the same trend as temperature has and we have data showing that the increase in greenhouse gases is correlated with the date when humans started releasing those greenhouse gases due to our own activity those three things together really show that it's human activity that's creating the warming