1. F=ma, Newton&#x27;s second law, can be replicated easily.  It&#x27;s a fact.
2. If I kick this soccer ball right here, applying a force, it will accelerate away from me.  It&#x27;s a fact.
3. Look, it has accelerated away from me, it&#x27;s a measurable fact!<p>...a short time later...<p>4.  Oh, I was standing at the bottom of a hill, so the ball just rolled back to my feet.<p>Do you understand?  We are discussing an insanely complex system, with feedback loops everywhere, and a scant (at best) 100 years of quality data on a planet 4 billion years old.  There is nothing simple about this.  The physics of the radiation balance isn&#x27;t in question, but for all we know it may be dwarfed by negative feedbacks.  They are forced to fallback on computer models for a reason.<p>Nobody talks about 99% of doctors and smoking, because we can empirically test this.  Hundreds of millions of people have smoked, and we have observed the effects.<p>The smoking&#x2F;cancer analogy always makes me smile, because it is actually a very good one.  Let&#x27;s turn it around.  The physics of how smoking causes cancer is pretty solid.  We know about toxins and carcinogens, etc.  But let&#x27;s say I hand you a single human being, and I ask you, &quot;if he smokes for the next 40 years, will he get cancer?&quot;.  We don&#x27;t have a freaking clue.  The human body - the feedback of the immune system defences, nutrition, genetics - are beyond our power to model.  Science is hopelessly unable to answer that question.  And ponder this for a moment - we have 6 billion potential test subjects to work with! We have one earth.  This is the state of climate science.  The biosphere&#x2F;atmosphere&#x2F;oceans&#x2F;etc. are every bit as complex as a single human body, and we have only one patient to study, and data for maybe 0.0000025 of the patient&#x27;s lifetime.<p>But, I hear you say, &quot;shouldn&#x27;t we be cautious then?  Shouldn&#x27;t we quit just in case?&quot;.  And fair enough, we probably should be cautious.  But the counterpoint to that is that fossil fuel usage isn&#x27;t a nicotine hit.  It doesn&#x27;t deliver us a few moments of pleasure in return for the risk of cancer.  It fuels our entire industrial civilization.  So the risk&#x2F;reward calculation looks quite a bit different, doesn&#x27;t it?<p>In one case, we have the potential risk confirmed by the empirical evidence of a test set of hundreds of million of smokers, and the potential reward being a nicotine hit.  In the other, we have no way of testing the theorized risk outside of models, and the reward is the energy to power our entire civilization.<p>So yeah, it is an analogy that always makes me laugh a little.