4 ms·

> the more extreme the weather anomaly, the less likely it is to be caused by human-induced (anthropogenic) global warming. Why is that the case? My knowledge

by rndn 11y ago

> the more extreme the weather anomaly, the less likely it is to be caused by human-induced (anthropogenic) global warming. Why is that the case? My knowledge is not based on much better sources than this blog post, but isn't the warming of the oceans believed to cause extreme weather anomalies?

tinco 11y ago
I think he's referring to the intuitive idea that how bigger the deviation the less likely it's caused by a small thing. Why should a 0.1C overall increase in temperature lead to a 5C degree difference this summer and the one 5 years ago? Much more likely is some larger timescale larger force dynamic. (Unless of course someone has proven a mechanism for the former). In the long run yes, warming of the earth will cause more extreme weather. But it has little relation to that of today.
- taylodl 11y ago
  If weather is known to be a nonlinear system then doesn't it make sense that climate would be as well? Why should we expect small changes in climate inputs to have correspondingly small changes in climate results?
  - jessaustin 11y ago
    There might be no reason to expect that, but they can't build models without that assumption, and they have to build models because they can't experiment. It's like looking for one's keys under the streetlamp.
    - kaybe 11y ago
      No, that's not how that works. You put in basic physics, which is known from experiments, and then there are assumptions about which effects have to be included - start with the big ones such as solar irradiation and ground IR radiation, and atmospheric stratification, and fluid dynamics and knowledge about air currents. Then add the ocean as a heat reservoir and ocean currents, ground albedo changes due to cover change (snow, desertification, crops...). Add some clouds in different heights. Oh, and stratospheric, tropospheric and ocean chemistry. Then add aerosols which influence cloud cover, vertical temperature distribution and thus winds, ... Of course, some variation in the solar irradiation due to changes in the sun and the Earth's orbit. And I probably forgot a lot of influences here which are already considered. Other important non-physical model parameters are things such as spatial grid size and time steps. Atm we are adding more influences to the models. It is thought that they have smaller impacts, but they might not have. All these above are things based in physics and the basic rules have withstood many experiments. But - how about methane fluxes into the atmosphere due to permafrost melting, or due to ocean heating? We are also not sure about many fluxes in nature because they are very hard to measure. Satellites help., but... How much methane do cows emit? There are halogenes coming out of the sea ice, why and how much is it, and what does it do to atmosperic chemistry? What processes take part in the soil and how much of what is emitted over the whole globe? Does it change with changing conditions, how much? There are many important questions in the details here, and you actually have to feed all of that into the models. This is where the assumptions are, because we do not know all of these things, and many more. And then you see what the result is. A small increase in overall temperature is not just that, it changes the vertical temperature profile, which changes circulation patterns (among other things). And then you have a different distribution of temperatures on the surface. That's what the models say, and that is what we can see in reality, thus the models are not that bad here. Of course, there is still some way to go until we can trust the more detailed results, I'd say.
  - tinco 11y ago
    Well, I'm not a weather expert. But to me climate is a whole bunch of weather, and a whole bunch of non-linear things don't always make a non-linear thing together. Molecules in a gas do weird stuff individually, but the gas as a whole behaves very predictably.
    - kaybe 11y ago
      Sadly, the main governing equations of weather (eg Navier–Stokes equation for fluid dynamics) are still very much non-linear. Non-linear does not mean unpredictable, it just means that it is very hard to solve (currently no analytical solution for the Navier–Stokes equation) and that, well, the system is not linear. (And it applies to gas, btw.) For weather, other important effects are phase change of water at given pressure/temperatures (which can store large amounts of energy), radiative transport (again, non-linear equation, not solved) and heat transfer (non-linear equation, solved (easy)). For forecasts, you also cannot measure the full state of the system at any point in time. This makes it a very hard problem - otherwise weather forecasts would have been perfect ages ago. With the advent of cluster computing and measurement satellites, it is now possible to improve the forecasts vastly, but it's still hard.

by rndn 11y ago

tinco 11y ago

I think he's referring to the intuitive idea that how bigger the deviation the less likely it's caused by a small thing. Why should a 0.1C overall increase in temperature lead to a 5C degree difference this summer and the one 5 years ago? Much more likely is some larger timescale larger force dynamic. (Unless of course someone has proven a mechanism for the former). In the long run yes, warming of the earth will cause more extreme weather. But it has little relation to that of today.

taylodl 11y ago
If weather is known to be a nonlinear system then doesn't it make sense that climate would be as well? Why should we expect small changes in climate inputs to have correspondingly small changes in climate results?
- jessaustin 11y ago
  There might be no reason to expect that, but they can't build models without that assumption, and they have to build models because they can't experiment. It's like looking for one's keys under the streetlamp.
  - kaybe 11y ago
    No, that's not how that works. You put in basic physics, which is known from experiments, and then there are assumptions about which effects have to be included - start with the big ones such as solar irradiation and ground IR radiation, and atmospheric stratification, and fluid dynamics and knowledge about air currents. Then add the ocean as a heat reservoir and ocean currents, ground albedo changes due to cover change (snow, desertification, crops...). Add some clouds in different heights. Oh, and stratospheric, tropospheric and ocean chemistry. Then add aerosols which influence cloud cover, vertical temperature distribution and thus winds, ... Of course, some variation in the solar irradiation due to changes in the sun and the Earth's orbit. And I probably forgot a lot of influences here which are already considered. Other important non-physical model parameters are things such as spatial grid size and time steps. Atm we are adding more influences to the models. It is thought that they have smaller impacts, but they might not have. All these above are things based in physics and the basic rules have withstood many experiments. But - how about methane fluxes into the atmosphere due to permafrost melting, or due to ocean heating? We are also not sure about many fluxes in nature because they are very hard to measure. Satellites help., but... How much methane do cows emit? There are halogenes coming out of the sea ice, why and how much is it, and what does it do to atmosperic chemistry? What processes take part in the soil and how much of what is emitted over the whole globe? Does it change with changing conditions, how much? There are many important questions in the details here, and you actually have to feed all of that into the models. This is where the assumptions are, because we do not know all of these things, and many more. And then you see what the result is. A small increase in overall temperature is not just that, it changes the vertical temperature profile, which changes circulation patterns (among other things). And then you have a different distribution of temperatures on the surface. That's what the models say, and that is what we can see in reality, thus the models are not that bad here. Of course, there is still some way to go until we can trust the more detailed results, I'd say.
- tinco 11y ago
  Well, I'm not a weather expert. But to me climate is a whole bunch of weather, and a whole bunch of non-linear things don't always make a non-linear thing together. Molecules in a gas do weird stuff individually, but the gas as a whole behaves very predictably.
  - kaybe 11y ago
    Sadly, the main governing equations of weather (eg Navier–Stokes equation for fluid dynamics) are still very much non-linear. Non-linear does not mean unpredictable, it just means that it is very hard to solve (currently no analytical solution for the Navier–Stokes equation) and that, well, the system is not linear. (And it applies to gas, btw.) For weather, other important effects are phase change of water at given pressure/temperatures (which can store large amounts of energy), radiative transport (again, non-linear equation, not solved) and heat transfer (non-linear equation, solved (easy)). For forecasts, you also cannot measure the full state of the system at any point in time. This makes it a very hard problem - otherwise weather forecasts would have been perfect ages ago. With the advent of cluster computing and measurement satellites, it is now possible to improve the forecasts vastly, but it's still hard.