I'm not sure about the technology used at the time, but the basic answer to your question that that they had a lot more thermometers than you expect, distributed globally too. And as we're discussing global averages, the noise about +-2F in your house isn't really the same problem.
Edit: Here's a neat 100-year reanalysis paper if you're interested. Abstract link here, full pdf available on the page: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-87-2-175. "Feasibility of a 100-Year Reanalysis Using Only Surface Pressure Data"
Seriously, our forecasts are nearly always wrong. So.....saying we can make as accurate of forecasts for 200 years ago...that's not really saying much.
This is after moving to two cities in the same state, more than 100 miles apart, the forecasts still never get better.
Also, if a meteorologist can't get the current state of the weather correct, why on earth would I trust his statement of what the temperature is going to be like? At that point I'm just going to consider it a guess.
In reality, the models are derived using different methods by different scientists.
I didn't reference centurial anything - I said that thinking it's a problem is not understanding variance. Climate scientists not only agree with me they say the same thing.
So at this point either put up some actual science or just stop JAQing off.
There are some pretty accurate forecasting services
You can make fun of meteorologists if you want, but they are not wrong 95% of the time. In fact, over the last 20 years the accuracy of predictions has gone WAY up on average. There are still many places where forecasting is difficult and it's going to be a long road to improve it to get people like you to trust the forecast. But we're improving and we're making the best forecasts we've ever made in the industry.
If it came off as me trying to be down on meteorologists, that wasn't my intent, and I can't edit my original post to reflect that, so hopefully you'll see my comment here.
It is saying quite a lot actually because the past has already happened. In the first case you are talking about the future, and yes, in some places weather is more unpredictable. You can of course move to the desert and enjoy clockwork predictable weather if it bothers you that much.
The OP was talking about "afcasting" though. In that case measurement have already been taken, but there are other records: ice cores, sea sediment, and many others. So it makes for a very interesting topic.
If your 2-3 day forecasting is off by 5-6 degrees (celcius), why would your "aftcasting" forecast for 200 years ago be any more accurate if it is "just as good" as a 2-3 day forecast? That means I would expect an error of 5-6 degrees, same as a 2-3 day forecast
edit: formatting
> For the beginning of the twentieth century, the errors of such upper-air circulation maps over the Northern Hemisphere in winter would be comparable to the 2–3-day errors of modern weather forecasts.
Might be worth reading the abstract / full paper if you're interested in the topic.
The article this discussion is linked to is claiming "1.46°F (0.81°C)" variance over recorded history. Recorded meaning they know what actually happened.
But I cannot believe that 2-3 day forecasts are accurate to within 2 degrees. Even the services linked by other commenters criticizing my original point claimed only 77% accuracy in the best case,
https://2cco2.wordpress.com/2015/08/04/the-difference-betwee...
I'd recommend at least writing a brief summary to the video if you really want to maintain an effective FAQ.
Meteorologists lower the quality of the data they receive.
People don't want bad news. People don't want to hear that it's going to rain on their weekend. People won't tune in to hear constant bad news.
So meteorologists take the positive and optimistic side.
The reality of forecasting is that much of the data, models, the warnings, are all created by the NWS.
The further you get from real NWS data, the lower the quality tends to be. It's like a game of telephone, except with forecasting.
National forecasters like The Weather Channel utilize tons of NWS data and models, and present it in a more friendly way. Generally there is a loss of quality here (and, when you look at TWC's buzzfeed approach to weather, it's not hard to see why they might respect clicks above all else).
Then, further down the pipe, away from the NWS and the actual source, away from National broadcasters, we get to local broadcasters. Once again, these guys are largely relying on upstream info, just packaging for the local audience.
It's not surprising that local meteorologists provide the lowest quality forecasting, because that's not really their job to provide highly accurate forecasting. Their job is actually to keep you watching through a commercial break, so the show remains on-air. The NWS is the service whose job is it to accurately forecast.
For example, just look at whatever near-term forecast you have handy. What are the forecast high and low temperatures for the next few days? What are the error bars on those highs and lows?
Oh, you couldn't find error bars? Yeah.
Where do you live? Every time I turn on the news its 90+% FUD.
It gets easier over longer periods of time. I may not be able to predict very well whether it's going to be 27 degrees C on July 17th 2016, but I can make a pretty good guess at the average temperature throughout the entire month, and I would be willing to put money down that it will lie within a relatively narrow band.
Folks have tried to get around this by finding proxies for temperature (measurements that are theorized to track temperature, like the width of tree rings for example), and then calibrating that data by comparing it with the intervals for which we have reliable data (since 1970 for satellite data, or earlier for whatever thermometer data might be suitable). The long-term trends are identified and argued based on these proxies.
So to answer your question, they can calibrate a proxy using the satellite record, see what it suggests about 1880, and combine that with the available temperature data, but that's about it.
[0] http://www.ncdc.noaa.gov/sotc/global/2015/5/supplemental/pag...