Calculate the doubling time for PNG in 1990 given a natural increase of 22 per 1000 people.

The provided text calculates the growth rate for PNG in 1990 as:

$$\text{Growth rate} = \frac{\text{Natural increase}}{1000} \times 100\% = \frac{22}{1000} \times 100\% = 2.2\%$$

The formula for Doubling Time is given as:

$$\text{Doubling Time} = \frac{70}{\text{growth rate per year}}$$

Using the growth rate of $2.2\%$ for PNG in 1990:

$$\text{Doubling Time} = \frac{70}{2.2}$$ $$\text{Doubling Time} \approx 31.818 \text{ years}$$

Rounding to one decimal place:

$$\text{Doubling Time} \approx 31.8 \text{ years}$$

The doubling time for PNG in 1990 is approximately $\boxed{\text{}31.8 \text{ years}\text{}}$