"Show me a climatologist who denies the Northern hemisphere in many/most parts got colder in the LIA."

Micheal Mann? And any climatologists who still do not realize that Mann's Hockey Stick is invalid.

A summary:

McKitrick: What the Hockey Stick Debate is About?
"The hockey stick debate is about two things. At a technical level it concerns a well-known study that characterized the state of the Earth's climate over the past thousand years and seemed to prove a recent and unprecedented global warming. I will explain how the study got the results it did, examine some key flaws in the methodology and explain why the conclusions are unsupported by the data."
http://www.climateaudit.org/index.php?p=166

"The issue is your regurgitation of an incorrect line, and then your subsequent claim to be "essentially correct". "

England was warmer and during these warmer periods grapes were commonly grown, during LIA it longer was no longer profitable/practical to grow grapes- and it became far less common to grow grapes. In current climate conditions in England it is becoming warm enough to grow grapes, and grape grower are expecting that there be warmer climate in the future that will allow better growing conditions for growing grapes.

When one is dealing a sizable region [such as england] there will areas in which have different climatic conditions, numerous factors can be involved to create these conditions. For example elevation can affect average temperature, as general rule every 1000' of higher elevation lowers temperature by 3 F. So even area of the size of small town due to changes in elevation you can differences of 3 F.
People who grow things might mention things like "having a southern exposure"- one can have acres of land which on average receive more sunlight than other areas. A river or even a creek can alter average temperature. The average of amount wind and the direction of the wind can make a big difference. And then of course people change the very local environment so plants have more a favorable condition- a greenhouse is typical example, but rock walls, mulch or compost can also have affects. A large pile of leaves or say 12" of dirt will stop most freezing- this why water pipes per building codes are buried to certain depth- if live in a colder region the pipes per code would buried deeper though it could get cold enough they may freeze despite this.