Their warfare, building and agricultural skills may have been impressive but, according to scientists in Peru, the Incas would have been nothing without good weather induced by climate change. The climate varies along the length of the trail. During the day it can be quite warm and sunny; dry during the first two days, and a little humid on the third and fourth days. In the night, the first two campsites are often very cold, while the third night is more temperate.
The climate can be divided into two seasons, wet and dry, although the weather varies depending of the region. During the coastal summer (late december to early April) the sky is often clear and weather is hot and sticky. This is the beach season.
In the second season which is the remaining of the year, the garúa, (coastal mist) moves in and the sun is rarely seen, plus the temperature drops, but it is not as cold as it is in the north of USA. April marks the beginning of autumn.
The rainy period begins at the end of November and lasts until March. Rains can be quite heavy at times. Although rain can make the hike a little more difficult, on the other hand, the landscapes benefit from the rain and are green and lush.
For the first 3000 years or so represented within the 8-metre section of lake sediments, the climate was relatively cold - the core contents dominated by rock and sandy fragments washed into the lake from the mountains.
Then, sediments from 800 AD were marked by evidence of an arid period including a drought lasting about 100 years, shown mainly by the appearance of sedge seeds that are normally found only at the fringes of the lake. The drought wiped out two rival cultures in the area: the Wari and the Tiwanaku. Then, around 1100AD came the lift in temperatures that gave the Incans such a boost.
With the tree line moving steadily higher up the mountains, the Incas carved terraces into the mountainside to grow potatoes and maize, and developed a system of canals to irrigate the land. The climate remained dry but melting glacial ice provided a constant supply of water, resulting in a surplus of crops to feed the population.
The meteoric rise of the Incan empire between 1400 and 1532 was driven by a sustained period of warmer weather, new research on Peruvian lake sediments suggests. The higher temperatures, starting around 1150, ended thousands of years of cold aridity, and enabled Incan farmers to build mountainside terraces for growing crops at altitudes previously too cold to support agriculture. The extra warmth, lasting around 400 years, also supplied extra water for irrigation in the shape of melt-water from Andean glaciers at higher altitudes.