There are several important questions since the Medieval Warming as AR5 admits today they cannot explain the warming that occurred in the 10^th century. (AR5 Section 10.7.1.1 Page 918)

Then in the 14^th century warming the IPCC notes it is possible natural forcing caused by the storage and transport of heat delayed the warming of the Southern Ocean. (AR4 Section 9.3.3.3 Page 683)

The IPCC refers to several books that looked at past climate change going back as early 1914. These books looked at things like the cooling in the 17^th century in parts of Iceland covered with ice. (AR4 Box 6.4 Page 468)

The IPCC notes an important question that the earth’s average temperature has not increased smoothly since 1900 as expected if just greenhouse gas were being increased. (AR4 Section 9.4.1.1 Page 683)

Here, the IPCC tries to answer important temperature questions.

AR4 states during the 1950s and 1960s global temperatures leveled off. They state this was caused by aerosols from fossil fuels and other sources like Mt. Agung eruption in 1963 ejecting material that blocked the sun. They state there has been a rapid warming since 1970 believing increases in greenhouse gases, not changes in other forcing, have been the primary cause. This is one of the IPCC primary lines of evidence for man responsibly for a warming the earth. (AR4 FAQ 9.2 Page 702)

The IPCC claims each of the last 3 decades the Earth’s surface is warmer than the one before with the warmest being warmer than any of the decades before 1850. (AR5 Forward Page V)

AR4 notes instruments have shown over the last century and half that surface temperatures went up .35°C from 1910 -1940 then again .5°C since the 1970s. (AR4 FAQ 3.1 Page 252)