Bullshit. You should always look at a period long enough to get rid of the noise. If you do that with ocean levels, you'll see that the long term trend is undeniably up.

https://upload.wikimedia.org/wikipedia/commons/0/0f/Recent_Sea_Level_Rise.png

You can also see that the short time data is very noisy.

The question was who we should trust climate scientists or historians. Between the two, I'd put my money on the climate scientists, given any reasonable definition of the term.

But of course, if you can find some good research done by a historian about the global temperature record, I'm sure people would be interested.

Modern farmers aren't just planting potatoes. Besides, if you want to make a point that the MWP was warmer than today, the data needs to be calibrated to an actual temperature, and the data needs to be global.

Anecdotes about Viking farming in Greenland provides neither.

Historians better get busy and get their asses back to Greenland, to document modern farming:

"Trees are growing and the fields are full of potatoes, lettuce, carrots and cabbage" to be sold at the local market, explains Anders Iversen, who heads a plant nursery near Qaqotorq in the south.

Temperatures are warmer now, with the mercury sometimes rising above 20 degrees Celsius (68 Fahrenheit) in summer, he says.

"If global warming continues, we will be able to grow even more kinds of vegetables during a longer season," he adds.

http://www.terradaily.com/reports/Global_warming_impacting_Greenlanders_daily_lives_999.html

Climate scientists, of course.

What historians are you talking about, and did they collect temperature data from all over the globe ?

How can a single rocket, a tube filled with pork, cost $10 billion? Please explain.

FTFY. Now the answer is obvious.

Back to the beginning: if a majority of scientists agree that the MWP was cooler than today, what would be a valid reason, for non-scientists, to assume the MWP was actually warmer ?

Yet, everybody agrees that earth has been cooling down since around 2000.

No, only a couple of crackpots agree on that. Here's a link of global temperature anomalies in tabular format:

http://data.giss.nasa.gov/gistemp/graphs/Fig.A2.txt

Average for 2000-2009 was +0.52
Average for 1990-1999 was +0.31
Average for 1980-1989 was +0.18

Doesn't look like it's getting colder, especially if you consider that every single year since 2000 has been warmer than the 1990-1999 average.

"majority" arguments don't work with science.

It doesn't work within science. It works fine when trying to determine policy based on science. Everything we teach the kids at school is based on scientific consensus. That's why we teach the theory of evolution, even though there are some people that disagree. Even if there's no guarantee that scientific consensus is correct, it's still the best thing we have.

Nobody's trying to outlaw CO2. People just want to prevent it from rising too far.

Keeping CO2 below 450 ppm isn't going to harm any plants, when it has been below 350 ppm for hundreds of thousands of years.

Imagine you're standing on the beach, and someone's telling you that flood is coming in. You're screaming they are wrong, because the sea has retreated in the last 2 minutes.

Are we clear now?

We are clear that you don't understand how to look at the data, yes.

Here's a start:

https://secure.wikimedia.org/wikipedia/en/wiki/List_of_weather_records

Notice how many heat records have been recorded since 2000, and how most cold records are much older.

And here's a paper describing the statistical relationship between climate and extreme weather:

http://www.pik-potsdam.de/~stefan/Publications/Nature/rahmstorf_coumou_2011.pdf

The CLOUD experiment supports current understanding, by showing that the cosmic ray effect is too small to create actual clouds. So what are you trying to say ?

And what's the alternative to scientific consensus ? Should we determine global policy by Tarot cards ?

If 2-sigma events happen on a regular basis, they are unlikely to be a result of chance.

If you make a list of extreme weather events, the number of broken heat records is much bigger than the number of broken cold records.

I agree that people overreact, and start blaming each event on global warming. That's not correct. However, looking at the increase of dozens of extreme weather events, it's fair to say that global warming is a likely factor behind many of them.

they would drive most of the world into poverty and a brutish existence

The same thing will happen if we just continue to burn fossil fuels. We can't keep producing them at current rate for much longer. The peak oil problem is likely more urgent than global warming, so an aggressive plan for transition would benefit us either way.

we have no idea about what the real benefits/disadvantages we would experience from +450ppm.

Sure, we have plenty of ideas.

But I see your point. Short term benefits outweigh long term doubts. Since, long term, we're all dead anyway, I can't argue with that.